Tag: Freshwater Fish Profiles

Eel reproduction is one of those topics where the more you dig in, the stranger and more fascinating it gets. I’ve kept eels in my saltwater tanks over the years, and even knowing the basic life history, it’s remarkable that despite centuries of scientific study, nobody has ever observed a European eel spawn in the wild. not once. The Sargasso Sea is where it’s believed to happen, but we’re still largely working from indirect evidence.

This isn’t just an academic curiosity. It has real implications for eel conservation, and it helps explain some strange behaviors you’ll notice in eel species kept in the aquarium trade. Here’s what science actually knows, what it doesn’t, and why the eel reproduction question has stumped researchers for as long as it has.

What Are Eels?

If you’re not familiar at all with eels, then they’ll initially look otherworldly. Are they fish? Are they snakes? Or are they something new altogether?

Don’t be fooled, these are actually thin, almost finless fish that belong to the Anguilliformes order. Within this scientific order are 8 suborders and almost 800 species! Both saltwater and freshwater eels belong to this scientific order, though not every fish that’s labeled as an ‘eel’ is a true eel!

If you are familiar with eels at all, then you may have heard of the electric eel (Electrophorus spp.) which is capable of delivering a deadly shock. While these fish certainly look like true eels, they are actually more closely related to knife fish as members of the Gymnotiformes order.

Although freshwater eels and saltwater eels look very different from each other and their related genera, there are a few defining features that make them true eels of the Anguilliformes order.

Anguilliformes are ray-finned fish. But unlike other fish, eels lack pelvic fins entirely and most species don’t have pectoral fins. Eels also have a conjoined dorsal and anal fin that makes a singular, long fin that extends across the latter half of their body. Interestingly, this evolution also allows these fish to swim backward. Another defining feature of eels is that some species have small scales while others have incorporated scales into their skin. Some may lack scales entirely.

Anglers and other eel-handlers especially note their ability to produce slime, which is a defense mechanism against predators and pathogens. Eels have sharp teeth fixed in their mouths, with some species having a second jaw known as the pharyngeal jaw. The first set of jaws is thought to specialize in catching the prey while the second set processes the food and moves it along to the digestive tract.

True eels can be found in freshwater and marine ecosystems around the world. Some species are catadromous which means that they migrate from one body of water to another. As we’ll see, some species of eel, especially those in the Anguillidae family, make extensive journeys from freshwater ecosystems to purely saltwater conditions.

An example of a true eel is the European freshwater eel. This species of freshwater eel lacks scales and breathes through its skin. This unique ability makes them able to survive out of water for up to 48 hours! European freshwater eels can also bury themselves and hibernate in the mud over the winter months; this is also needed when their natural habitats dry out over the summer.

Where Do They Come From?

Fish have been around for a long time which means that they’ve been studied for a long time. So much so that even ancient Greek philosophers devoted their entire lives to understanding their origins, especially the beginnings of eels and their reproductive processes. Surprisingly, the great Aristotle contributed much thought to these lifecycles.

According to Aristotle, eels materialized from mud and were actually a type of earthworm. This became a popular theory as no one had ever seen eels reproduce and there was no other reasonable explanation; this also eliminated the need to explain their apparent absence of reproductive organs.

It’s hard to believe that this exact explanation for eel reproduction persisted for over 2,000 years, but few dared to challenge the findings of Aristotle.

It wasn’t until Pliny the Edler, a Roman naturalist and natural philosopher, theorized another answer to eel reproduction. He believed that new eels were born from the old shed skins of parent eels that scratched themselves on hard surfaces, like on the seafloor and on rocks. Each scraping would turn into a new eel.

Other popular beliefs included eels being born from sea foam or from when sunlight reflected off the surface of the water in just the right way. Some even thought that eels hatched on the rooftops of great buildings or derived from the gills of other fish. The more absurd theories mentioned the involvement of beetles and hair from horses falling into the river.

Many centuries later, famous psychoanalyst Sigmund Freud took a stab at uncovering the mystery of eel reproduction. In 1876, while a medical student at the University of Vienna, Freud bought as many eels as possible. After 400 dissections, Freud finally located the male eel’s gonads deep within the abdominal cavity, dispelling any previous theories!

Geography

This was a major breakthrough in understanding eel reproduction and their lifecycle.

You might be saying to yourself that you’ve never actually seen an eel in the wild. This isn’t because eels aren’t abundant, but rather because they’re reclusive and nocturnal.

When not migrating thousands of miles, these fish like to stay as elusive as possible, cramming themselves into tight caves and rock formations, burying themselves in the substrate, or even living together in communities known as eel pits.

In freshwater ecosystems, they can be found on nearly every continent excluding Antarctica in rivers, lakes, streams, and even ponds. Keep in mind that some eels are able to move across land, allowing them to enter isolated areas of water. Marine eels have a much larger range and can be found in most regions of the ocean at varying depths.

How Do They Reproduce?

The long-asked and long-evaded question: how do eels reproduce? Even today, after thousands of theories and anatomical dissections, there are many unknowns about the lives of eels.

To help understand how eels reproduce, we need to first look at the 5 incredibly complex stages of an eel’s life cycle.

5 Stages Of Their Life Cycle

The lifecycle of an eel is divided into 5 distinct stages. Each one marks different biological and sexual maturity levels of the eel. Most notably, sex organs develop in the later stages.

1. Larvae
2. Glass Eel
3. Elver
4. Yellow Eel
5. Silver Eel

You can see an illustration of the life cycle in the photo below (Wikipedia photo source)

The Larvae

The first stage of an eel’s lifecycle is the larval stage, individually known as leptocephalus. In this phase, the baby eel emerges from its fertilized egg in or near its species’ breeding grounds.

Leptocephalus are largely transparent. They have radically compressed bodies with minimal muscles and organs. One of their most defining features is a simple stripe that runs down the middle of their pane-like body. During the next metamorphosis period from larva to glass eel, the transparent gel changes into solid adult tissue.

Interestingly, leptocephali feed on marine snow and other organic matter to facilitate growth. They are largely planktonic and depend on ocean currents to get them to where they need to go, mostly estuaries and other safe coastal ecosystems. Once in an intertidal region, they begin their transformation into glass eels.

Glass

The transformation from leptocephalus to glass eel is both a geographical and physical change. As leptocephali, eel larvae live in the ocean. As they begin their metamorphosis into glass eels, they must make their way into protected estuaries where freshwater and saltwater ecosystems mix. This is a challenging move and many eels do not survive due to their lack of control over their navigation.

Physically, leptocephali start to change into more recognizable glass eels. One of the major changes during this life stage is the development of pigmentation which takes over the previous clear gel. But underneath their skin, there is another major change happening.

A regular fish’s body needs to osmotically adapt to changes in salinity, like the differences between freshwater and saltwater conditions; typically, when marine fish enter brackish water, their cells begin to swell as there is a difference in osmotic pressure. Eels have evolved to combat this problem with specialized kidneys that are able to retain more salt to better match their internal salinity to their external salinity.

Elvers

The next stage of an eel’s life cycle is the elver stage. This is the pre-adult stage that occurs once the eel is about 2 to 3 years old. The elver will have dark yellow pigmentation and reach up to 8 inches in length. If they’ve not already made their way upstream to freshwater rivers and streams, then young elvers will begin their journey.

At this point, the eels are omnivores and will try to eat anything they can fit into their mouth. This largely includes crustaceans, worms, and insects. Elvers and the next lifecycle, yellow eels, can stay in these freshwater upstream regions of rivers for up to 20 years until they are mature enough to migrate back out to the ocean. Many eel species return to the Sargasso Sea to spawn, though this varies by species.

Sadly, elvers are a very popular dish that has caused issues with eel sustainability in the past.

Yellow

Before becoming a silver eel, or an adult eel, elvers must first become a yellow eel. This is when the pigmentation turns even darker and their true adult colors start to form, including brown, olive green, yellow, and black. These colors will largely depend on environmental factors, such as temperature and turbidity. At this point, juvenile eels can measure over 30 inches in length.

Yellow eels will continue to live in and move from one freshwater ecosystem to the next until they’re ready to transform into their final life stage, the silver eel.

Silver or Adult

Believe it or not, not much is known about adult eels, also known as silver eels. Scientists aren’t sure what determines when eels transition into their final form. This is even more complicated by being unable to tell how old an eel is by its appearance alone at this point. One thing is understood though, eels aren’t considered fully mature until they develop sex organs in the last stage of their life cycle as an adult eel.

As adult eels, males can reach 2 feet in length while females can grow up to 4 or more feet. They change drastically in color from dark natural colors to steel silver. Only as adults is when eels are mature enough to make the trip to the Sargasso Sea or other spawning grounds depending on the species.

How Do They Mate In The Wild

When talking about eel reproduction, you’ll often hear about the Sargasso Sea. The Sargasso Sea encompasses Bermuda (including the infamous Bermuda Triangle), the Azores, and the West Indies. This area of the Atlantic Ocean is a 2-million-square-mile span of saltwater that is home to the breeding grounds of millions of eels. Most notably, freshwater European and American eels make this thousand-mile journey.

When male and female eels arrive at their specific breeding grounds, it is believed that eels reproduce through external fertilization. This means that the females release millions of eggs that then get fertilized by the males’ sperm. Sadly, the adult eels die soon after. The eggs then get fertilized and repeat the previous lifecycles, making their way back to North America and Europe respectively. Other species of eel have different, yet still specific breeding grounds.

Different Types

Remember, there are 800 species of known eel around the world! Imagine how many there are undiscovered if scientists couldn’t even identify their sexual organs for thousands of years.

The truth is that a lot is still unknown about eels and new species are still being discovered. Even the species that we have documented are not fully understood.

Here are some of the most well-known species of freshwater eel.

European

The European eel is a common type of freshwater eel that can live to be 85 years old in the wild and 55 years old in captivity! Unfortunately, they are listed as a critically endangered species due to overfishing, parasites, and other human activity.

These fish feature a pair of small pectoral fins and have the typical snake-like body. They grow to between 2 to 3 feet in length. As catadromous fish, European eels spend their adult lives in freshwater rivers and streams throughout much of Europe and migrate to saltwater conditions to reproduce. This particular species travels to the Sargasso Sea in the Atlantic Ocean.

Interestingly, European eels don’t stop traveling upstream until they’re sexually mature. They’ve been found in seasonal ecosystems that dry up over hot months and in isolated lakes and ponds, confirming their ability to travel over land and to survive for extended periods buried in the substrate.

Many breeding programs have been installed to help declining numbers of the European eel with slight success using hormones and controlled conditions.

Shortfin and Longfin

Two more common types of eels originate from New Zealand: the longfin eel (Anguilla dieffenbachii) and the shortfin eel (Anguilla australis). The longfin eel is endangered while the shortfin eel is near threatened.

Like European eels, longfin and shortfin eels can live for a considerably long time. They are found in freshwater streams and lakes and make their way to regions in the Pacific Ocean for spawning. Longfin eels are found further inland in New Zealand than shortfin eels, but shortfin eels can also be found in several other countries across the South Pacific.

These two fish also have different breeding grounds. Longfin eels travel to areas near Tonga while shortfin eels migrate to deep waters around New Caledonia. Every female can produce up to 20 million eggs!

Longfin eels are aptly named for their lengthy fins. Their dorsal fin is almost two-thirds the length of their body. Shortfin eels have a similar appearance but have a fin that starts farther away from the head. Another difference is that when a longfin eel bends, wrinkles form on its skin; a shortfin eel’s skin will remain smooth. Females are notably larger and live longer than males.

Japanese

Japanese eels (Anguilla japonica) are mainly found in Japan, Korea, China, and Vietnam. Like the other types of eel on this list, Japanese eels also spawn in the sea but spend a large majority of their lives in freshwater.

When the time comes, Japanese eels travel to the North Equatorial Current in the western North Pacific. Throughout this long journey, Japanese eels do not eat. Instead, they collect all the nutrients they need through a specialized oil before making the trip.

These fish feature a dull grey, brown, and greenish dorsal on top of a white underbelly, though these colors depend on environmental factors.

Sadly, Japanese eel populations are decreasing due to changing ocean temperatures, habitat loss, and fluctuating salinities. Japenese eels are also a popular culinary dish, popularly known as unagi, though regulations have been implemented to reduce overharvesting and to encourage supplementation. As a result, they are listed as an endangered species.

The African Longfin

The African longfin eel (Anguilla mossambica) is another common type of eel, though not much is known about them. They have olive, gray, and black bodies with a light underside. They prefer fast currents in the western Indian Ocean off of Africa.

They eat a variety of fish and invertebrates, but will also scavenge.

Difference Between Freshwater and Saltwater

There are freshwater eels and there are saltwater eels, but most freshwater eels spend some time in saltwater conditions. Where marine eels live in the ocean can vary, with some preferring coastal lagoons and others enjoying the open sea. Some species even dig into the mud and sand.

The major difference between freshwater and saltwater eels is body texture and appearance. Freshwater eels have a firmer texture, while saltwater eels are softer and leaner. Most saltwater eels are also much more colorful than freshwater eels, making them a very popular addition to the marine aquarium.

For the adventurous eel connoisseur, freshwater and marine species also have different tastes.

How Do They Survive Migration?

You might be wondering how eels survive for thousands of miles as they transition from freshwater to saltwater. What do they eat? When do they sleep? How do they know where to go?

In fact, most eels don’t eat on their way to their final destination. In most cases, their stomach deteriorates. The blood vessels around the swim bladder increase for additional support while swimming. Their eyes also double in size, which increases sensitivity to blue waves of light, increasing their ability to see in the dark. Their kidneys also adapt to hold more salt to increase internal salinity levels to compensate for their surrounding salinity changes.

European eel migration is one of the longest migrations documented by any marine creature. They typically start their migration in autumn and arrive at the Sargasso Sea in late winter and spring. This journey is approximately 3,000 miles long and can range from 80 to 170 days.

It is believed that eels use every sense they have to navigate their journey. It’s also strongly believed that they rely on lunar cycles and wait for the perfect conditions in regard to temperature, salinity, tides, and currents, to make their move.

What About Captivity?

Because of their complex lifecycles, eels have not been bred in the home aquarium. Many researchers and hobbyists have attempted artificial breeding, but nothing can replicate the years spent in freshwater, transition to saltwater, and external fertilization.No one has ever seen captive eels breeding in a home aquarium. They have a complex life cycle, and their sexual organs only develop at the last stage. Also, they spend months and years traveling to the spawning ground present in the Sargasso Sea, where once eel eggs and sperm are realized, the fish die. Those free-floating eggs get externally fertilized.

That isn’t to say that researchers aren’t close, though. In fact, some species of eel have been successfully bred in closely monitored systems with the help of hormones and fluctuating parameters. However, the full lifecycle of an eel has never been achieved in captivity.Many people tried different artificial ways to breed mature eels in a home aquarium but to no avail.

Their Lifespan

Eels are very hard to kill. They are built to withstand extreme differences in environmental conditions and have a very long lifespan. Their blood is poisonous and they have been known to swim for hours on end even with their head cut off.

However, any traces of toxic ammonia, nitrite, or nitrate in the aquarium can cause your freshwater or saltwater eel to succumb to unfavorable environmental factors.

FAQs

Closing Thoughts

Eels are some of the most complex aquatic creatures but you wouldn’t know that from their simple snake-like appearance. For years, it was impossible to know the complex life stages these fish go through while transitioning from freshwater to saltwater. While we’re still not exactly sure how eels go through these stages and make their migrations, we will make those dissections over time.

Do you have any theories about how eels reproduce? Let us know your thoughts below! Let us know your thoughts below! Subscribe to our YouTube channel for more crazy videos.

An African cichlid tank is not a community tank with colorful fish. It’s a controlled aggression system — and the moment you forget that, fish start dying. After 25+ years in this hobby and time managing retail fish stores, I’ve seen more bad stocking decisions in cichlid tanks than almost anywhere else. The rules for tank mates here are not suggestions. They’re the difference between a thriving display and a body count.

If you’re thinking of adding “a few peaceful fish” to soften the tank — don’t. That’s not how this works.

The good news: there are species that reliably work. Synodontis catfish are native to the same African rift lake systems and are the gold standard companion. Rainbowfish, large plecos, and carefully chosen cichlids from the same lake round out the short list. Here’s what you need to know before you stock anything.

Introduction To African Cichlids

African cichlids originate from some of the oldest freshwater lakes in the world — Lake Tanganyika, Lake Malawi, and Lake Victoria. These lakes are isolated ecosystems where species have undergone millions of years of divergent evolution, adapting to different depths, territories, and niches. The result is a group of fish that are as diverse as they are aggressive.

There are over 2,500 known members of the Cichlidae family worldwide, with many more unnamed and undiscovered. The African species kept in the hobby are primarily from Lake Malawi and Lake Tanganyika — and they do not share tanks gracefully.

It’s no wonder African cichlid aquariums are so popular. These fish are bold, colorful, and behaviorally fascinating. But their care requirements — especially regarding tank mates — are not forgiving.

What People Get Wrong

The most common mistake is treating an African cichlid tank like a community tank that happens to have aggressive fish. People add dithers, bottom dwellers, or “tough” fish hoping they’ll survive in the margins. Sometimes they do — for a while. Then breeding season hits, or a dominant male establishes a hierarchy, and the body count starts.

The second mistake is mixing African cichlids from different lakes. Lake Malawi mbuna and Lake Tanganyika species have overlapping water chemistry requirements, but their behavioral patterns are completely different. Tanganyikan shell dwellers and substrate spawners need structured, calm zones. Malawi mbuna are relentless, constant-movement fish that destroy those zones on sight.

The third mistake is understocking. In an African cichlid tank, more fish is often safer — not because they tolerate each other, but because aggression gets spread across more targets. A tank with three cichlids will have one dominant fish that kills the other two. A tank with twelve gives the dominant fish too many targets to fixate on any one.

Stocking A Tank

A standard African cichlid setup starts at 55 gallons (208 L), though 75 gallons (283 L) gives significantly more room to manage aggression. Decoration should be rock-heavy — stacked to create caves, territories, and broken sight lines. Cichlids rearrange everything, so anchor what you can.

Substrate should be bare bottom or crushed coral — both help buffer the pH up toward the 7.8–8.5 (ideally 8.0–8.2) range African cichlids need. Avoid live plants; cichlids will uproot them within days.

If you plan to add non-cichlid tank mates, you need at minimum 125 gallons (473 L). Many of the compatible species — plecos, large catfish, rainbowfish in schools — need volume to avoid the constant line of sight cichlids maintain.

Things To Consider

Before you add anything to an African cichlid tank, run through three questions — and be honest with yourself on all three.

1. Can it handle the water? Cichlids need hard, alkaline water: pH 7.8–8.5, hardness 10–20 dGH, temperature 76–82°F (24–28°C). Most freshwater fish come from soft, acidic rivers in South America or Southeast Asia. They won’t crash immediately in high-pH water — they’ll just slowly decline. You’ll think they’re fine, then one day they’re not.

2. Can it handle the aggression? Cichlids establish territories and defend them viciously, especially during spawning. Slow fish, small fish, and unarmored bottom dwellers are targets. If a cichlid can catch it and it can’t fight back, it’s either food or a punching bag.

3. Will it blow up the hierarchy? Every new fish triggers a re-establishment of the pecking order. That process involves chasing, fin nipping, and sometimes killing. Add fish in groups, add them all at once if possible, and rearrange the rockwork when you do — that resets territory claims and reduces targeted attacks on the newcomers.

The Biggest Mistake

Adding one or two of the “wrong” fish to an established cichlid tank, hoping they’ll find a quiet corner. They won’t. A lone rainbowfish in an mbuna tank is a meal waiting to happen. A single Synodontis without hiding spots gets cornered. The fish that work as tank mates work because of group dynamics, specific positioning, and tank size — not because they’re tough enough to survive individually.

I’ve watched hobbyists lose hundreds of dollars in fish trying to create a “mixed community” in a cichlid tank — and I’ve seen it happen at the store level too, where customers would bring fish back after a week, bewildered at what went wrong. It doesn’t work. You either build the tank around the cichlids and choose mates that fit the system — or you end up with dead fish and a lesson learned the hard way.

Reality of Keeping an African Cichlid Tank

This is not a set-it-and-forget-it tank. Cichlid keepers check on their fish daily because the social dynamics shift constantly. A fish that was fine yesterday can be the target of coordinated harassment tomorrow if a dominant male decides to rearrange his territory.

Spawning changes everything. A breeding pair of mbuna will terrorize every other fish in the tank — including fish twice their size. I’ve moved fish out of cichlid tanks at 10pm because a pair decided to spawn and the rest of the tank was taking damage. You need to be prepared to remove fish, add dividers, or rearrange the tank on short notice. These aren’t edge cases. This is routine cichlid management.

Here’s what the day-to-day actually looks like: the dominant male patrols his rock formation constantly, flaring at rivals and displaying full color when he’s confident. At feeding time, the whole tank goes from structured hierarchy to chaos — fish sprinting in every direction, lower-ranked individuals darting for scraps between the dominant fish’s rushes. Within a few weeks, you can predict which fish owns which corner of the tank. It’s a living social map, and it changes every time you rearrange the rocks or add a new fish.

The reward is a tank that looks like nothing else in freshwater. High color, constant movement, visible personality — African cichlids know their keeper. They’ll display for you, react to your presence, and establish routines. But you have to manage the system. It doesn’t run itself.

The Best Tank Mates

There are a few reliable options once tank size, water conditions, and aggression levels have been matched. Here are the species worth considering — with honest notes on each.

Expert Take

Having worked with African cichlids for 25+ years, including managing store tanks packed with them, my advice is blunt: stop trying to build a community around these fish. I’ve had African cichlid tanks work beautifully and I’ve had them turn into war zones — the difference was always stocking density and territory structure, not which tank mates I chose. In my experience with African cichlid setups, overstocking intentionally is counterintuitive but it works. The fish are beautiful but territorial, aggressive, and constantly rearranging the social order. The secret to a stable tank isn’t finding the “right tank mates” — it’s overstocking deliberately, using rock formations to break sight lines, and accepting that some fish will get beaten up. You’re managing a dynamic system, not picking peaceful companions. — Mark Valderrama, AquariumStoreDepot

Quick-Reference Comparison Table

1. Other African Cichlids

The best tank mates for African cichlids are other African cichlids — from the same lake. This is where most setups work long-term. But mixing cichlids from different genera, different aggression levels, or different lakes is where things fall apart.

African cichlids originate from massive lakes where populations of the same species might never interact. The behavioral differences between species from opposite ends of Lake Malawi are significant. Size, activity level, and aggression strategy all vary — and you have to match those variables carefully.

Key rules for mixing African cichlids:

• Match aggression levels — don’t pair highly aggressive mbuna with peaceful peacocks
• Stock multiple females per male (3–4:1 ratio) to distribute aggression
• Stick to one lake — Malawi or Tanganyika, not both
• Add all fish at the same time when possible, and rearrange rocks to reset territories
• Choose fish with different coloration — cichlids target fish that look like them

Popular genera for Malawi setups include Melanochromis, Pseudotropheus, Aulonocara, and Labidochromis. Tanganyikan setups commonly feature Neolamprologus, Cyphotilapia, and Julidochromis. It is very common to keep species-only tanks featuring peacock cichlids (Aulonocara spp.), hap cichlids, or mbuna.

How many can you keep? A standard 55-gallon (208 L) mbuna setup typically holds 10–15 cichlids. The key is deliberate overstocking — enough fish that no single individual becomes a constant target. Underpopulate an mbuna tank and the dominant male will kill everything else.

2. Jewel Cichlid

Ease: 6/10 — Works, but requires more careful management.

• Scientific name: Hemichromis bimaculatus
• Temperament: Semi-aggressive (becomes extremely aggressive when spawning)
• Origin: Western Africa
• Size: 6 inches (15 cm)
• Minimum Tank Size: 75 gallons (283 L)
• Diet: Omnivore
• pH: 7.0–8.0
• Temperature: 75–82°F (24–28°C)

The jewel cichlid is one of the most attractive African cichlids available — bright red with iridescent blue flecks. At baseline, they’re semi-aggressive and manageable. When spawning, they become a different animal entirely. Jewel cichlids will fight to the death to defend their young, and they attack fish far larger than themselves during that period.

Hobbyists have found success keeping jewels with more aggressive mbuna species — the mbuna’s constant pressure keeps the jewels from settling into a dominant breeding mode. This isn’t a recommendation; it’s a tradeoff. Understand what you’re signing up for before adding jewel cichlids to an established mbuna tank.

3. Paratilapia polleni

• Scientific name: Paratilapia polleni
• Temperament: Aggressive to smaller fish
• Origin: Madagascar
• Size: 12 inches (30 cm)
• Minimum Tank Size: 75 gallons (283 L)
• Diet: Omnivore (naturally piscivorous)
• pH: 6.5–8.0
• Temperature: 75–82°F (24–28°C)

Sometimes called the starry night cichlid, Paratilapia polleni is a relatively peaceful East African cichlid — relative being the operative word. These endangered, speckled near-black fish are the last surviving species of their genus and can be difficult and expensive to source.

The key issue: Paratilapia polleni grows to 12 inches (30 cm) and is naturally piscivorous. Any fish that can fit in its mouth will eventually end up there. Tank mates need to be large enough to be safe from predation. With appropriately sized companions, this species holds its own in an African cichlid system.

4. Synodontis Catfish

Ease: 7/10 — The closest thing to a guaranteed winner in a cichlid tank.

• Scientific name: Synodontis spp.
• Temperament: Peaceful
• Origin: Africa (including Lake Tanganyika and Lake Malawi populations)
• Size: Varies (typically 4–10 inches / 10–25 cm depending on species)
• Minimum Tank Size: 55 gallons (208 L)
• Diet: Omnivore
• pH: 7.5–9.0
• Temperature: 75–82°F (24–28°C)

Synodontis catfish are native to the same African rift lake systems as the cichlids — which is exactly why they work. They evolved alongside these fish, adapted to the same hard, alkaline water, and occupy a different layer of the water column (bottom vs. mid-to-upper). Cichlids generally leave them alone because they don’t compete for the same territory.

In my experience, Synodontis are the single most reliable non-cichlid fish you can add to one of these tanks — I’ve kept them with mbuna for years without a single issue. The best species for cichlid tanks include the cuckoo catfish (Synodontis multipunctatus), dwarf lake Synodontis (Synodontis petricola), and the Malawi squeaker (Synodontis njassae). Keep them in groups of at least 3–4 — they prefer company and behave better in small shoals. Give them plenty of caves and rock structure to retreat into. They’re nocturnal and will spend most of the day hidden; that’s normal behavior, not stress.

5. Rainbowfish

Ease: 7/10 — Surprisingly effective as a dither fish when kept in proper schools.

• Scientific name: Melanotaenia spp.
• Temperament: Peaceful
• Origin: Australia and New Guinea
• Size: 4–5 inches (10–13 cm)
• Minimum Tank Size: 55 gallons (208 L) for a cichlid pairing
• Diet: Omnivore
• pH: 7.0–8.0
• Temperature: 75–82°F (24–28°C)

Rainbowfish are one of the few genuinely peaceful fish that can coexist with African cichlids — not because they’re tough, but because they’re fast and move in coordinated schools. A school of 8–10 Boeseman’s rainbowfish (Melanotaenia boesemani) creates enough movement that cichlids can’t easily isolate an individual. They also function as dither fish — their open-water swimming signals safety to the cichlids and actually reduces overall aggression in the tank.

Not all rainbowfish work here. Boeseman’s is the standout choice: large enough not to be eaten, fast enough to evade cichlid aggression, and tolerant of harder water. I’ve seen a school of 10 Boeseman’s completely change the energy of an mbuna tank — the cichlids were still territorial, but they had less time to fixate on any single target. Avoid smaller rainbowfish species — they’ll be targeted. A single rainbowfish in a cichlid tank doesn’t survive. The school is the protection mechanism.

Hard Rule: Never mix Lake Malawi and Lake Tanganyika species in the same tank. The water chemistry overlaps, but the behavioral dynamics do not. Tanganyikan shell dwellers and substrate spawners will be relentlessly harassed by the larger, dominant Malawi mbuna. Pick one lake and build the tank around it.

6. Pleco Fish

Ease: 7/10 — Solid choice when sized correctly relative to the cichlids.

• Scientific name: Hypostomus spp., Ancistrus spp.
• Temperament: Peaceful
• Origin: South America
• Size: Varies — 4–18 inches (10–46 cm) depending on species
• Minimum Tank Size: 125 gallons (473 L) for larger species
• Diet: Algae, biofilm, occasional meaty foods
• pH: 7.0–8.0
• Temperature: 75–82°F (24–28°C)

Plecos are armored, bottom-dwelling fish from South America that have adapted well enough to hard, alkaline water that they work in African cichlid setups. They occupy the substrate, rarely compete with mid-water cichlids for territory, and their bony armor gives them meaningful protection against cichlid aggression.

Chosen plecos need to be large — at least several inches at introduction. A juvenile bristlenose in a cichlid tank gets beaten up. A full-grown common pleco (Hypostomus plecostomus) or large bristlenose holds its own. The 125-gallon minimum applies when pairing with larger cichlid species — the pleco needs escape routes and resting zones the cichlids don’t control.

7. Red Tail Shark

Ease: 6/10 — The most conditional option on this list. Know the limitations before adding one.

• Scientific name: Epalzeorhynchos bicolor
• Temperament: Semi-aggressive to aggressive
• Origin: Thailand
• Size: 4–6 inches (10–15 cm)
• Minimum Tank Size: 55 gallons (208 L)
• Diet: Omnivore
• pH: 6.5–7.5 (upper end required for cichlid compatibility)
• Temperature: 75–82°F (24–28°C)

The red-tail shark is the most conditional option on this list. It’s fast, territorial, and can hold its own in a cichlid tank — but only at the pH overlap point of about 7.5. African cichlids prefer 7.8–8.5; red-tail sharks top out around 7.5. That’s a narrow window, and keeping pH at 7.5 long-term means the cichlids are at the bottom of their comfort range.

Red-tails are also frequently confused with the rainbow shark (Epalzeorhynchos frenatum) at the store level — make sure you’re buying what you think you’re buying. These freshwater sharks work best with less aggressive African cichlid species. Pair one with dominant mbuna and you’ll have constant conflict. Read the full red tail shark profile before committing.

Fish To Avoid

More fish fail in African cichlid tanks than succeed. The combination of high pH, high hardness, and extreme aggression eliminates the vast majority of common freshwater species. Here are the most common wrong choices:

Most Community Freshwater Fish

Most freshwater community fish originate from soft, acidic South American or Southeast Asian rivers. Tetras, barbs, rasboras, danios — these fish are incompatible on two levels. First, they deteriorate in high-pH, hard water over time. Second, cichlids treat small, schooling fish as prey. The cichlid doesn’t see a school. It sees targets.

A freshwater community tank is also structured differently — planted, dense with hiding spots, relatively calm. An African cichlid tank is open, rocky, and constantly active. Community fish don’t thrive in that environment even before the cichlids start targeting them.

Goldfish

Goldfish are coldwater fish that need temperatures under 72°F (22°C). African cichlids need 76–82°F (24–28°C). These fish don’t share a viable temperature range. Add the high waste output of goldfish to the high aggression of cichlids and you have a tank that’s simultaneously dangerous and poorly filtered. Fancy goldfish in particular are slow-moving and would be immediately targeted.

Koi

Same reasons as goldfish — coldwater fish that belong in ponds, not tropical cichlid tanks. The temperature incompatibility alone ends the conversation.

Corydoras Catfish

Corydoras look like survivors — bottom dwellers, fast movers, safety in numbers. People try them all the time. They don’t work. Corydoras need soft, acidic water and temperatures in the lower 70s°F (low-to-mid 20s°C). That’s the opposite of what an African cichlid tank runs. Even if they could tolerate the water, they’d still be small, slow, and unarmored in a tank full of fish that are none of those things. They get hurt. They get eaten. They don’t belong here.

South and Central American Cichlids

South American cichlids — Mikrogeophagus, Apistogramma, Symphysodon — prefer soft, acidic water and are far less aggressive than African cichlids. Pairing them is almost always a disaster. The African cichlids bulldoze the water parameters and the South Americans simply don’t have the aggression to compete.

Large Central American cichlids (Oscars, Jack Dempseys, Dovii) can hold their own behaviorally — but they need soft, acidic to neutral water that is chemically incompatible with an African cichlid system. I’ve seen it done — a heavily buffered tank held at pH 7.4–7.5 where both sides survive. But that’s expert-level management, the parameters are a compromise for everyone involved, and it’s not a starting point. Don’t build your first cichlid tank around it.

Mark’s Pick: For a Malawi mbuna tank, the best “tank mate” approach is to stock multiple species at the same aggression tier. Pseudotropheus, Labidochromis, and Melanochromis in appropriate ratios — with 3–4 females per male — create enough social pressure that no single fish becomes the permanent target. Add them all at once, rearrange the rockwork, and let the hierarchy establish itself. That’s the system that actually works long-term.

Frequently Asked Questions

Can I keep African cichlids with community fish?

No. African cichlids need hard, alkaline water (pH 7.8–8.5) that most community fish can’t tolerate, and their aggression level makes peaceful coexistence impossible. The combination of parameter mismatch and territorial aggression eliminates virtually all standard community species from consideration.

Can I mix Lake Malawi and Lake Tanganyika cichlids?

No. While the water chemistry is similar, the behavioral dynamics are not compatible. Malawi mbuna are relentless, high-aggression fish that harass the more structured, territory-respecting Tanganyikan species. The mixing almost always results in Tanganyikan fish being bullied to death or chronic stress. Pick one lake and build around it.

How many African cichlids should I keep in a 55-gallon tank?

A 55-gallon (208 L) mbuna setup typically holds 10–15 cichlids. Deliberate overstocking is the key — enough fish that aggression gets spread across multiple targets rather than fixating on one individual. An understocked mbuna tank is a more dangerous tank, not a safer one.

What is the best non-cichlid tank mate for an African cichlid setup?

Synodontis catfish — specifically Synodontis multipunctatus or Synodontis petricola. They’re native to the same African rift lake systems, adapted to identical water parameters, occupy the bottom of the tank rather than competing for mid-water territory, and cichlids largely leave them alone. Keep them in groups of 3–4.

Can I keep a pleco with African cichlids?

Yes, with conditions. The pleco needs to be large enough not to be bullied — a juvenile bristlenose in an mbuna tank will take damage. A full-grown common pleco or large bristlenose holds up well. You also need a 125-gallon (473 L) tank or larger if you’re pairing big cichlids with big plecos — both need space they don’t share.

Will rainbowfish survive in an African cichlid tank?

Boeseman’s rainbowfish (Melanotaenia boesemani) can work in a large tank when kept in a school of 8–10. Their speed and coordinated movement make them difficult targets. They also function as dither fish, reducing overall cichlid aggression. Don’t attempt this with smaller rainbowfish species — they won’t last. And never add a single rainbowfish. The school is the survival mechanism.

Who Is This Setup Right For?

Good Fit If:

• You want a high-activity, high-color display tank and can manage ongoing aggression
• You have a 75+ gallon (283+ L) tank with substantial rock structure and broken sight lines
• You’re prepared to remove, rehome, or separate fish when aggression escalates
• You want to keep species-appropriate cichlids from one lake — Malawi or Tanganyika
• You understand that “tank mate management” is an ongoing part of this hobby, not a one-time decision

Avoid If:

• You want a peaceful community tank — African cichlids are not community fish
• You plan to mix delicate, slow-moving, or small fish — they will die
• Your tank is under 55 gallons (208 L) — aggression management requires volume
• You’re not willing to monitor the tank daily during the first weeks after any new introduction
• You want fish from different African lakes to coexist — it doesn’t work reliably

Final Thoughts

An African cichlid tank is one of the most visually impressive things you can do in freshwater. High color, constant activity, genuine personality — these fish deliver on all of it. But the tank mate question has one real answer: you’re not looking for peaceful companions. You’re building a system where aggression is managed through density, structure, and smart species selection.

The short list of what works — other same-lake cichlids, Synodontis catfish, large plecos, Boeseman’s rainbowfish in schools — is short for a reason. Everything else either can’t survive the water parameters or can’t survive the cichlids. Respect that list and your tank will thrive. Ignore it and you’ll be relearning the lesson the expensive way.

Build the system right and nothing in freshwater looks like it.

📘 Want to learn more? This article is part of our complete Freshwater Fish Guide — your ultimate resource for freshwater species, care tips, tank setup, and more.

Oscars are the fish that eat your other fish. I say that upfront because the number one mistake I see with oscar tank mates is people underestimating just how large and predatory these cichlids get. A juvenile oscar at the fish store looks manageable. by the time it hits 10 to 12 inches in a year or two, it will eat anything that fits in its mouth and bully anything that doesn’t. That means tank mates need to be big, tough, and ideally from similar South American river environments. I’ve seen oscars housed with small plecos, tetras, and even medium-sized cichlids. it rarely ends well. The picks that actually work long-term share one trait: they’re large enough that the oscar doesn’t see them as food and confident enough not to get pushed around. Here are 10 that have the best track record.

Introduction To Oscar Fish

Before we jump into the best tank mates for Oscars, we need to understand how oscar fish behave by themselves and with others. These are one of the most dynamic and charismatic fish in the freshwater aquarium hobby and are often referred to as water puppies.

The oscar fish is a large species of South American cichlid scientifically known as Astronotus ocellatus¹. These fish are regularly sold as juveniles when they are only just a couple of inches big. Their bright colors and ‘easy’ care requirements make them popular among unknowing beginner hobbyists. The truth is that oscar fish can grow to be over 18 inches long and live to be 20 years old.

Oscar fish are not beginner fish and should only be kept in large tank setups. That means that adding tank mates would require an even bigger setup.

Tank Requirements

Alone, an oscar fish requires a 75-gallon tank setup. A 125-gallon aquarium is preferred to give your fish more room to swim and to keep water parameters balanced. Oscar fish are messy eaters and can create a lot of waste, so a large and efficient filtration system is definitely required.

Otherwise, oscar fish have simple tank requirements. They need some structure for protection in the form of rocks or driftwood. A sandy substrate is preferred to allow your fish to burrow and arrange its home as it sees fit. Regular tank maintenance is a must to keep waste levels down.

As you can see, oscar fish are big, messy fish. Add more oscars or other fish species into the mix and you’re looking at a relatively demanding system. Many hobbyists are successful at keeping other fish with oscars despite their needs, though.

Do They Need Tank Mates?

The question at hand is, do oscar fish even need other tank mates at all?

The answer is no.

Oscar fish don’t get lonely and can happily entertain themselves. As mentioned before, these fish are the puppies of the freshwater aquarium hobby and can be personally interacted with in ways that can’t be done with other species.

There are a few ways that oscar fish can be given enrichment:

1) Create a dynamic aquarium setup. One of the best ways to keep your oscar fish engaged is by giving it an intricate home. Use rocks and driftwood to create burrows and tunnels. Regularly shift items around to keep your fish guessing what comes next without kicking up the substrate too much. This gives your fish different ways to recreate and rearrange its new home.

2) Introduce new items. On top of moving objects around, add new pieces and remove old ones. Some hobbyists even add cheap live plants that can be uprooted and eaten for an additional treat. Other alternatives include plastic floating balls and air stones.

3) Feed live food. Another great way to enrich your oscar fish is by giving live food every now and then. These freshwater fish have a big appetite and will eat even when they’re not hungry, though we don’t recommend overfeeding them! Oscar fish will happily take worms, brine shrimp, and even live fish and snails; use caution when introducing live fish and snails, as they can carry parasites.

4) Make feeding time exciting in addition to feeding live food and make dry foods exciting to eat. Oscar fish are known for waiting at the surface of the water for food and responding to objects (including fingers) entering the tank. Some Oscars can be trained to do simple tricks before they are fed. Food can also be placed in feeding mechanisms that make the fish work for its meal.

5) Add tank mates. Lastly, oscar tank mates may be added to the aquarium, including other Oscars. This provides constant interaction and reaction between the fish.

Top 10

If you have the space and filtration to consider possible tank mates for oscar fish, then you will need to decide which species best fit your system. Oscar fish aren’t particularly aggressive fish, but they need to be paired with large species that can tolerate being investigated and nudged from time to time.

Here are some of the best oscar tank mates available for a large freshwater fish tank setup!

1. Other Types

• Scientific name: Astronotus ocellatus
• Temperament: Semi-aggressive
• Origin: South America
• Size: 18 inches
• Minimum Tank Size: 75 gallons
• Diet: Omnivore
• pH: 6.0-8.0
• Temperature: 75-82°F
• Difficulty to breed: Difficult

Oscar fish might not seem like schooling fish, but they can sometimes be found in small groups throughout their natural habitat in the Amazon River basin. These fish can be kept in a loose school setting, given the right aquarium conditions.

By themselves, oscar fish do not appear to be schooling fish at all. They happily explore the tank by themselves and feel comfortable out in the front of the aquarium alone. But given the space and the numbers, oscar fish will move together in a loose school.

This is best achieved in a large tank with similar-sized fish introduced together.

What Size Tank Do You Need For 2?

It is not recommended to keep only 2 Oscars together. It is very difficult to tell males apart from females, which could lead to a combination of two males. While not overly aggressive fish, two male oscar fish will definitely fight.

Unless the two fish are a known breeding pair, oscar fish should only be kept by themselves or in a group.

How Many Can Live Together?

Given unlimited space, there is no limit to how many oscar fish can live together. Eventually, even a large group would dissipate into smaller groupings.

For a captive-kept group, 7 oscar fish is ideal. This will require at least a 300-gallon tank.

There is a big difference in temperament between a solitary oscar and a shoal of Oscar. Oscars that live alone are very playful and responsive to their owner’s actions. A group of Oscars is much mellower and uniform in their intentions.

2. Blood Parrots

• Scientific name: Hybrid
• Temperament: Semi-aggresssive
• Origin: Not naturally occurring
• Size: 8 inches
• Minimum Tank Size: 55 gallons
• Diet: Omnivore
• pH: 6.5-8.0
• Temperature: 72-80° F
• Difficulty to breed: Mostly infertile

Not the most popular oscar pairing; the blood parrot is extremely popular on its own. This is a hybrid species created by selectively breeding different types of cichlid, mainly species from Central America. Blood parrots are largely infertile as a result.

The problem with blood parrots as tank mates for oscar fish is the difference in demeanor. Blood parrots are physically inflated and have limited movement and speed. Oscar fish have strong tail fins that can easily overcome a blood parrot.

Still, some hobbyists have made this pairing work as long as neither of them is an overly aggressive fish.

3. Silver Dollars

• Scientific name: Metynnis spp.
• Temperament: Peaceful
• Origin: Southeast South America
• Size: 6 inches
• Minimum Tank Size: 30 gallons
• Diet: Herbivore
• pH: 5.0-7.0
• Temperature: 72-77°F
• Difficulty to breed: Easy

If you’re looking for tank mates that will form true schools, then silver dollars are a good choice for an oscar tank. Beware that these peaceful fish get much bigger than you might expect, with individuals growing to be 6 inches each. This means that a school of six can quickly max out a big tank.

It’s also important to note that silver dollars are active fish. They might have a small minimum tank size on their own, but they excel when given plenty of horizontal space to swim.

Silver dollars are one of the best fish species for Oscars due to their size and agility. They are also exclusively herbivores, which can make feeding them and your Oscars separately that much easier.

4. Green Terror

• Scientific name: Andinoacara rivulatus
• Temperament: Semi-aggressive
• Origin: Southeast South America
• Size: 8 inches
• Minimum Tank Size: 55 gallons
• Diet: Omnivore
• pH: 6.5-8.0
• Temperature: 75-80°F
• Difficulty to breed: Moderate

The green terror cichlid is similar in shape, size, and needs to the oscar fish. These two fish have similar demeanors, which helps prevent bullying; juvenile green terror cichlids are more likely to get picked on by older Oscars, so it’s recommended to get them both while they’re the same size.

In most cases, a green terror cichlid and oscar is the best combination available without having a monster fish tank. A 125-gallon tank will fit both of these fish very comfortably. However, temperaments between individual fish can vary, so it’s important to have a backup plan if one needs to be removed.

5. Jack Dempsey Fish

Jack Dempsey Fish” class=”wp-image-553072″/>

• Scientific name: Rocio octofasciatum
• Temperament: Aggressive
• Origin: Central America
• Size: 10 inches
• Minimum Tank Size: 55 gallons
• Diet: Carnivore
• pH: 6.5-8.0
• Temperature: 75-82°F
• Difficulty to breed: Moderate

The Jack Dempsey cichlid is one of the most popular and well-known species of freshwater fish available. These are big, colorful fish that have fierce personalities. There are several varieties of Jack Dempsey available for even more heightened coloration.

Jack Dempsey cichlids are a good tank mate option for most oscar setups. These are aggressive fish that grow to be around the same size as Oscars and can hold their own in a fight. Still, fighting is not ideal and can lead to injury and eventual death.

The best way to increase compatibility between a Jack Dempsey cichlid and an oscar is by picking individuals that are similar in size and introducing them into the aquarium at the same time. This leaves equal opportunity for territories to be claimed.

Also, do not buy a breeding pair of Jack Dempsey as they will become incredibly aggressive toward all other fish in the aquarium.

6. Giant Gourami

• Scientific name: Osphronemus goramy
• Temperament: Generally peaceful
• Origin: Southeast Asia
• Size: 18+ inches
• Minimum Tank Size: 200 gallons
• Diet: Herbivore
• pH: 6.0-8.0
• Temperature: 68. 86°F
• Difficulty to breed: Difficult

The giant gourami isn’t commonly seen in the aquarium hobby anymore, but–if you’re able to get your hands on one–could be a great choice for a large oscar tank. Simply put, giant gouramis are giant and can easily surpass 2 feet in length. Surprisingly, they’re relatively peaceful fish that intimidate Oscars out of sheer size; mature giant gourami has been known to become more aggressive as they age.

In some ways, the giant gourami is the best tank mate species for Oscars as their calm demeanor also calms down the Oscars. Giant gouramis have also been known to relax overly dominant male Oscars.

7. Arowanas

• Scientific name: Osteoglossinae subfamily
• Temperament: Semi-aggressive
• Origin: South America
• Size: 2.5 feet
• Minimum Tank Size: 250 gallons
• Diet: Carnivore
• pH: 6.0-7.0
• Temperature: 75-82°F
• Difficulty to breed: Difficult

Arowanas, most commonly the silver Arowana (Osteoglossum bicirrhosum), are regularly kept in oscar tank setups–if you have the space for a potentially 3-foot fish. Arowanas are one of the most unique fish species available in the aquarium hobby.

Arowanas have downward-pointing mouths that create a trapdoor for prey on the surface. This behavior keeps them at the surface of the aquarium, which means they’re less likely to interact with the Oscars below.

Arowanas aren’t always big, though; smaller ones can make the perfect snack for a larger oscar. When buying an Arowana, make sure that it can’t easily fit into the mouth of your oscar.

What Bottom Feeders Can Live With Oscars?

It’s always ideal for picking tank mates that don’t cohabitate at the same levels of the tank. That’s one of the reasons why the surface-dwelling Arowana is a great choice for an oscar tank setup. Luckily, there are a few potential oscar tank mates to fill up the bottom of the tank too.

8. Clown Loaches

• Scientific name: Chromobotia macracantha
• Temperament: Semi-agressive
• Origin: Southeast Indonesia
• Size: 12 inches
• Minimum Tank Size: 75 gallons
• Diet: Omnivore
• pH: 6.0-7.5
• Temperature: 72-82°F
• Difficulty to breed: Rarely documented

Clown loaches might not seem like they could be oscar tank mates, but that’s because many hobbyists fail to realize their potential mature size. The clown loach can grow to be over a foot in length. Add on the fact that these loaches need to be kept in schools of at least 6 or more, and you have a pretty demanding fish.

On top of its size, the clown loach is a semi-aggressive fish that will defend its place at the bottom of the tank. They are also a good tank mate choice for Oscars as they will sift through the substrate and help pick up any food that is missed from the messy eaters above.

9. Common Pleco

• Scientific name: Hypostomus plecostomus
• Temperament: Generally peaceful
• Origin: South America
• Size: 20 inches
• Minimum Tank Size: 125 gallons
• Diet: Omnivore
• pH: 6.5-7.5
• Temperature: 72-82°F
• Difficulty to breed: Difficult

The common pleco might be seen as a small bottom-dwelling fish to the unknowing hobbyist, but these fish are monsters. The common pleco can grow to be at least 20 inches at full size and live for a long time.

Common plecos are commonly seen in nano community tanks but do best in monster-fish setups or ponds. Though a suckerfish is capable of clinging to vertical surfaces, they tend to stay on the bottom of the substrate, which means that they’ll stay out of the way of their oscar tank mate. In addition, they’ll help clean up any uneaten food.

Common plecos are typically peaceful. However, they’ve been known to cling onto the sides of other fish and become aggressive to species that venture too far to the bottom.

10. Freshwater Stingrays

• Scientific name: Potamotrygonidae family
• Temperament: Semi-aggressive
• Origin: Mainly South America
• Size: Varies
• Minimum Tank Size: 180 gallons
• Diet: Carnivore
• pH: 6.5-7.5
• Temperature: 75-82°F
• Difficulty to breed: Moderate

Freshwater stingrays might not be the first tank mates you think to add to your oscar tank, but they’re one of the best if you have the space and legal permits. Freshwater stingrays are generally easy to care for but require a lot of space and a high-quality protein diet.

Picking the right species is also important to consider in regard to tank size. Here are some of the most popular freshwater stingrays available in the hobby:

• Ocellate river stingray/Moto stingray (Potamotrygon Motoro)
• Bigtooth river stingray/P12 (Potamotrygon henlei)
• Black diamond stingray (Potamotrygon leopoldi)

Though carnivores, stingrays will likely avoid going after live fish; they prefer their natural diet of mollusks and crustaceans. That means that, for the most part, your Oscars and stingrays will live independent lives in the same tank even though they originate from similar areas of the world.

Oscar Tank Mates at a Glance

Final Thoughts

Oscars are great fish with tons of personality that can be kept on their own, in a school, or with other tank mates. There is a large selection of oscar tank mates available to the casual hobbyist or the committed enthusiast, with the usual determining factor being space and diet.

These are monster fish that need monster tanks! But as long as their basic needs are met, then both oscar and their oscar tank mates will live together successfully.

Fish to Avoid Entirely with Oscars:

• Any fish under 6 inches (15 cm) — will be eaten once the oscar reaches adult size
• Long-finned or slow-moving species (angelfish, fancy guppies, bettas) — easy targets
• Aggressive but smaller cichlids (convicts, firemouths) — will be bullied relentlessly
• Delicate catfish under 8 inches — will not survive oscar aggression at the substrate

Neon tetras were probably one of the first fish I ever kept, and 25+ years later they’re still among my favorites for a well-planted community tank. A school of 15. 20 neons moving through a planted setup catches the light in a way that genuinely doesn’t get old. They’re also about as peaceful as fish come, which gives you a lot of flexibility with tank mates.

The main consideration is size. Neons are small (under 1.5 inches), and anything large enough to fit one in its mouth eventually will. Beyond that, you want peaceful fish that can share soft, slightly acidic water without outcompeting neons at feeding time. In the neon tetra tanks I’ve run, the biggest mistake was always school size, people understock and then wonder why their neons look washed out and stressed. Here are 15 tank mates that reliably work.

Choosing NEON TETRA Tank Mates – A Word Of Caution

Neon tetras get along with loads of other tropical fish, but there are just as many species that don’t make good tank mates. So how do you choose?

Size

Neon Tetras are very small fish with a maximum size of about 1.25 inches. At this size, many larger fish can (and will) swallow them whole!

Most popular aquarium species are omnivorous or carnivorous fish, so choosing similar-sized tank mates is always a good idea. There are exceptions, but most fish that grow over 3 or 4 inches will be risky.

Neon tetras can be housed in tanks as small as 10 gallons on their own, but bigger is better if you want to keep more than one species. 15 gallons will work, but 20+ is a better bet when setting up a community tank.

Group Size

Group or school size is another important factor to consider when choosing neon tetra tank mates.

You will notice that the fish species in this article are small, up to 2 inches. Fish of that size might not need very much room, but these species are social creatures that need to be kept with their own kind to behave confidently.

Parameters

Neon tetras prefer slightly cooler water than most other tropical fish. They also enjoy mildly acidic water. These are important factors when choosing tank mates because some fish need colder or warmer conditions or water with a higher pH.

Let’s take a look at the ideal parameters for your neon tetras:

• Water Temperature: 68 – 78 °F
• pH: 5 – 7
• Hardness: 18 – 215 ppm
• Flow: Low to Moderate

Temperament

Neon tetras are peaceful fish, and they need peaceful tank mates. Avoid territorial fish or species that are known to be aggressive or nip fins. Be aware that even peaceful fish can behave badly if they are not kept in groups or if they are under stress.

Swimming Level

It’s a good idea to add fish that occupy various levels in the water column. This article focuses on colorful schooling and shoaling fish, but adding a few bottom feeders will help to keep your tank clean while adding another layer of movement.

Top 15 Companions

Now that you know what to look for in the perfect neon tetra tank mate let’s jump in and meet 15 amazing species you can add to your fish tank. Take note of the following facts and guidelines for each species:

• Scientific Name
• Adult Size
• Care Level
• Temperament
• Swimming Level
• Minimum Tank Size
• pH
• Water Temperature

Let’s get started!

Expert Take

After 25+ years keeping and selling freshwater fish, neon tetras remain one of the species I have the most opinions about, because I’ve seen how badly they fail when the setup is wrong. They’re one of the most forgiving community fish in the hobby when the conditions are right, and one of the most fragile when they’re not. They need a mature, stable, soft water tank with no aggressive fish. I see more neon tetra deaths from stress and aggression than from any disease. I’ve seen neon tetra schools thrive for years and I’ve seen them crash in weeks, the difference is almost always school size and water maturity, not bad luck. Pick tank mates that are genuinely peaceful, similar in size, and compatible with soft, slightly acidic water. — Mark Valderrama, AquariumStoreDepot

Quick-Reference Comparison Table

1. Other Types

Ease: 9/10. One of the safest choices for this tank setup.

Neon Tetra

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One of the most popular freshwater community schooling fish available in the aquarium trade. Great neon blue colors!

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• Scientific Name: Paracheirodon innesi
• Adult Size: 1.25 inches
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Middle
• Minimum Tank Size: 10 gallons
• pH: 5 -7
• Water Temperature: 68 – 78 °F

Sometimes, the best tank mates for neon tetras are other neon tetras! These peaceful tropical fish are very social creatures that live in large schools in their natural habitat.

There is no limit to the number of neon tetras you can keep if you have enough room, but you should keep a minimum of 6. Like other schooling aquarium fish, your neon tetras just won’t be comfortable without the company of their own species.

2. Black

Ease: 9/10. One of the safest choices for this tank setup.

Black Neon Tetra

A variant neon variety. More reliant than neon and cardinal tetras

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• Scientific Name: Hyphessobrycon herbertaxelrodi
• Adult Size: 1.5 inches
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Mid/ top-water
• Minimum Tank Size: 15 gallons
• pH: 5 – 7.5
• Water Temperature: 72 – 77 °F

Black neon tetras are a different species from regular neon tetras, but they have very similar behavior. Their bold black, silver, and red colors contrast with the blues of the neon tetras for an amazing display.

Black neon tetras are true community fish. They grow slightly larger than regular neon tetras, but you can easily keep a small school of both species in a 15-gallon tank with good filtration and plenty of swimming space.

3. Green

Ease: 9/10. One of the safest choices for this tank setup.

Green Neon Tetra School” class=”wp-image-1067276″/>

• Scientific Name: Paracheirodon simulans
• Adult Size: 0.75 – 1 inch
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Mid/ top-water
• Minimum Tank Size: 10 gallons
• pH: 5 – 6.5
• Water Temperature: 76 – 95 °F

The green neon tetra is very similar to the regular neon, but it stays a little smaller. These little fish have even brighter blue and green coloration but have less red than regular neon tetras.

Green neons can make great neon tetra tank mates, but they prefer warmer water. That means the two species must be kept right around 77°F to keep everyone happy.

4. Dwarf Rasbora

Ease: 7/10. Good choice with a few conditions to watch.

• Scientific Name: Boraras maculatus
• Adult Size: 0.75 – 1 inch
• Care Level: Moderate
• Temperament: Peaceful
• Swimming Level: Mid/ top-water
• Minimum Tank Size: 10 gallons
• pH: 5 – 6.5
• Water Temperature: 68 – 82 °F

The dwarf rasbora (video resource) is a tiny fish from Southeast Asia. They are very peaceful fish that will thrive in a well-maintained community tank with neon tetras and other smaller fish.

The dwarf rasbora is a good tank mate for a heavily planted aquarium. These fish can thrive in a small tank, but maintaining excellent water quality in a low volume of water is best left to more experienced aquarists.

5. Exclamation Point Rasbora

Ease: 7/10. Good choice with a few conditions to watch.

Exclamation Point Rasbora

One of the smallest fish available in the hobby. Best in schools and easy to care for

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• Scientific Name: Boraras urophthalmoides
• Adult Size: 0.5 – 0.75 inches
• Care Level: Moderate
• Temperament: Peaceful
• Swimming Level: Mid/ lower levels
• Minimum Tank Size: 10 gallons
• pH: 6 – 7
• Water Temperature: 68 – 82 °F

The exclamation point rasbora is a true nano fish and one of the smallest freshwater fish in the aquarium hobby! These tiny schooling fish get their name from the dot and stripes on the sides of their body.

Exclamation point rasboras are good neon tetra tank mates in a heavily planted aquascape. They are ideal for more advanced aquarists looking for a nano community fish.

Hard Rule: Never add neon tetras to a tank with fish significantly larger than them. Anything that can fit a neon in its mouth (angels, large cichlids, large barbs) will eventually eat them. And neons that survive being chased will live in constant stress, which kills them slowly.

6. Harlequin Rasbora

Ease: 9/10. One of the safest choices for this tank setup.

Harlequin Rasbora

A peaceful schooling fish. An ideal community fish. A great beginner fish

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• Scientific Name: Trigonostigma heteromorpha
• Adult Size: 1.5 – 1.75 inches
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Mid/ top-water
• Minimum Tank Size: 15 gallons
• pH: 5 – 7.5
• Water Temperature: 70 – 82°F

Looking for a hardy fish with great color and personality for your neon tetra community tank? Look no further than the harlequin rasbora! These beautiful fish make quite a statement with their bold black triangular markings.

Harlequin rasboras will get along great with your neon tetras, but it’s very important to keep them with other fish of their own species. Pick up a group of at least 8 of these active fish.

7. Celestial Pearl Danio

Ease: 7/10. Good choice with a few conditions to watch.

Celestial Pearl Danio

A great-looking danio fish. Males are more colorful than females. A midway dwelling fish

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• Scientific Name: Celestichthys margaritatus
• Adult Size: 0.75 inches
• Care Level: Moderate
• Temperament: Peaceful
• Swimming Level: Mid/ lower levels
• Minimum Tank Size: 10 gallons
• pH: 6.5 – 7.5
• Water Temperature: 68 – 78°F

Celestial pearl danios (AKA galaxy rasboras) are very suitable tank mates for neon tetras in a well-maintained home aquarium. These little fish are very peaceful, but they are easily outcompeted for food by larger active swimmers, so choose their tank mates carefully.

You will love the way these shoaling fish hang out and display for each other. They are not exactly coldwater fish, but they enjoy the same cooler water temperatures as neon tetras.

8. Cherry Barbs

Ease: 9/10. One of the safest choices for this tank setup.

Cherry Barb

A popular freshwater fish from the barb family. One of the most peaceful barb fish

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• Scientific Name: Puntius titteya
• Adult Size: 1.75 – 2 inches
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Mid/ top-water
• Minimum Tank Size: 15 gallons
• pH: 6 – 8
• Water Temperature: 68 – 80 °F

Cherry barbs are a great nano community fish from the same family as goldfish. They are a very peaceful barb species that won’t bother your neon tetras.

These schooling fish come from forest streams in Asia, and they thrive in community tanks with other peaceful schooling fish.

Cherry barbs are very active swimmers, and they need the company of their own species to feel comfortable. Keep a group of at least 6 in a tank with plenty of swimming space, and you’ll find that they make great tank mates for your neon tetras!

9. Dwarf Gourami

Ease: 7/10. Good choice with a few conditions to watch.

• Scientific Name: Trichogaster lalius
• Adult Size: 3 inches
• Care Level: Moderate
• Temperament: Peaceful
• Swimming Level: All levels
• Minimum Tank Size: 15 gallons
• pH: 6 – 7.5
• Water Temperature: 72 – 80°F

Dwarf Gouramis are active and curious fish that enjoy exploring their aquarium. These fascinating fish breathe air at the surface of the tank, so keep that in mind if you plan on growing floating plants.

The male dwarf gourami is a very colorful fish with iridescent blues, reds, and silvers – just like your neon tetras! These fish should be kept in pairs or small groups.

10. Honey Gourami

Ease: 7/10. Good choice with a few conditions to watch.

Honey Gourami

One of the more peaceful Gourami fish available in the hobby. Has a unique yellow coloration and only grows up to 2 inches in length

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• Scientific Name: Trichogaster chuna
• Adult Size: 2 inches
• Care Level: Moderate
• Temperament: Peaceful
• Swimming Level: All levels
• Minimum Tank Size: 15 gallons
• pH: 6 – 7.5
• Water Temperature: 72 – 80 °F

The honey gourami is similar to the dwarf gourami but stays even small at around 2 inches. These peaceful tropical fish will brighten up your aquarium with their beautiful golden color.

Honey gouramis are easy to care for, so they make a great choice for beginner fish keepers looking for a new species with an interesting shape and calm personality. You can keep a pair of these fish in a tank of 15 gallons but jump up to 20 gallons or more if you want a small group.

11. Sparkling Gourami

Sparkling gouramis (video source) are also known as pygmy gouramis. They are one of the smallest gourami species in the aquarium hobby, and they are a great choice for your neon tetra tank.

They are more streamlined than other gouramis, and their large fins and bright blue eyes really make them stand out in a tropical community. Sparkling gouramis are not exactly schooling fish, but they prefer to be kept in a group with their own species.

12. Amano Shrimp

Ease: 7/10. Good choice with a few conditions to watch.

Best Shrimp For Planted Tanks!

Amano Shrimp

Best For Planted Tanks!

When it comes to keeping a healthy planted aquarium, Amano Shrimp are the best. These hard-working crustaceans will dutifully wipe your plants and rockwork clean of algae. Their appetite for different types of algae that can’t be matched by other shrimp breeds!

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• Scientific Name: Caridina multidentata
• Adult Size: 2 inches
• Care Level: Moderate
• Temperament: Peaceful
• Swimming Level: Bottom
• Minimum Tank Size: 10 gallons
• pH: 6 – 7.6
• Water Temperature: 60 – 80°F

Amano shrimp are one of the larger freshwater shrimp species in the aquarium hobby. These shrimp are named after Takashi Amano, the legendary aquarist and photographer.

Amano Shrimp are amazing algae eaters, which makes them the perfect choice for planted aquariums. They may not be the most colorful inverts, but they are fascinating to watch.

Adults are generally safe with neon tetras and other small fish, but shrimplets can be risky. Providing plenty of hiding spaces and dense plants like Java moss will give them a safe place to hang out until they are large enough to explore.

13. Cherry Shrimp

Ease: 9/10. One of the safest choices for this tank setup.

Beginner Friendly

Cherry Shrimp

Great red color and very hardy. Cherry shrimp are the best beginner shrimp for shrimp tanks

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• Scientific Name: Neocaridina davidi
• Adult Size: 1.25 – 1.5 inches
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Bottom
• Minimum Tank Size: 5 gallons
• pH: 6.8 – 7.5
• Water Temperature: 65 – 80 °F

Cherry shrimp are popular, hardy, and affordable freshwater shrimp that can be great neon tetra tank mates. These bottom feeders eat algae and other waste, which makes them a natural choice for your clean-up crew!

Adult cherry shrimp are usually safe to keep with neon tetras, but the babies will be eaten if they don’t have plenty of hiding places like caves and fine-leaved plants. You may wish to add a few inexpensive ghost shrimp first to see if your fish are going to be shrimp-safe.

14. Nerite Snail

Ease: 9/10. One of the safest choices for this tank setup.

Best Algae Snail

Horned Nerite Snail

Horned Nerite Snails are excellent algae eaters for planted tanks.

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• Scientific Name: Neritina spp.
• Adult Size: 1- 1.5 inches
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Bottom
• Minimum Tank Size: 5 gallons
• pH: 6.5 – 8.5
• Water Temperature: 65 – 85 °F

Nerite snails are beautiful and hardworking members of your clean-up crew. These colorful creatures cruise around on the leaves of plants and your aquarium glass, slowly grazing on algae to keep your tank looking great.

Nerite snails do not breed in freshwater, so you don’t have to worry about them multiplying in your tank. Many amazing species are available in the aquarium trade, with zebra and tiger nerites being the most popular.

15. Mystery Snails

Ease: 9/10. One of the safest choices for this tank setup.

• Scientific Name: Pomacea bridgesii
• Adult Size: 2 inches
• Care Level: Easy
• Temperament: Peaceful
• Swimming Level: Bottom
• Minimum Tank Size: 5 gallons
• pH: 7 – 8.4
• Water Temperature: 68 – 82°F

Mystery snails are another great invertebrate option for your neon tetra tank. These large snails come in a variety of colors, including white, golden, purple, and blue.

These snails lay their eggs outside of the water, so you don’t have to worry about them breeding if you keep your tank full. Mystery snails can be kept with neon tetras if you have water right around neutral but they do not thrive in low-pH conditions.

Other Possibilities

Want even more neon tetra tank mate ideas? These fish are also potential choices:

• White cloud minnows
• Bristlenose plecos
• Kuhli loaches
• Corydoras catfish
• Zebra danios

Fish To Avoid

Now that we’ve covered a bunch of great neon tetra tank mates let’s take a look at some of the tank mates you should avoid.

In over 25 years in this hobby, the species that caused the most problems with neons weren’t always the obvious predators, it was the mid-size, semi-aggressive fish that people thought were “probably fine” that did the real damage.

• Severums
• Any large, aggressive fish
• Aggressive cichlids

Most of the fish listed above are examples of larger fish that can eat your neon tetras. Avoid fish that grow larger than about 3 inches to stay on the safe side.

Betta fish aren’t going to eat neon tetras, but they can be a little aggressive toward them. The least risky will be female bettas. Other small aggressive fish like tiger barbs and silvertip tetras should also be avoided as well as any species that require water temperatures above 78 °F or a pH above 7.

Community Tank Tips

Have you chosen your favorite neon tetra tank mates? Before you go out and order your new fish, take a few minutes to read through these handy neon tetra tank tips!

Tank Size

You can keep neon tetras in a tank of just 10 gallons, but your options are pretty limited. I would suggest a tank of at least 15 gallons, but 20 gallons or more is advisable. Remember, neon tetras are schooling fish, so you’re going to want at least 6.

If you add some other schooling aquarium fish like harlequin rasboras, your total stocking will increase to at least 14 fish.

Bigger is (almost) always better when setting up a community tank, so keep this in mind if you don’t already have your aquarium set up.

Filtration, Lighting & Heating

A successful neon community tank requires good filtration, a reliable aquarium heater, and six to eight hours of lighting each day.

Neon tetras do not mind a decent flow rate in their tank since they live in rivers in their natural environment. Nevertheless, they are small fish that will become stressed if forced to swim against a strong current all day.

Decorating Your Tank

Your Neon Tetras will enjoy plenty of swimming space, but they prefer to have some structure in their home. Add some driftwood and rocks to create a more natural habitat.

Growing live plants in your aquarium is a great way to improve your water quality and make your tank even more beautiful.

Choose easy plants like Java ferns and Amazon sword if you’re just starting out. These plants don’t need any specialized equipment to thrive.

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Feeding Your Fish

Neon tetras are very easy to feed. Providing high-quality flake food once or twice each day will keep them happy and healthy. Provide the occasional treat like live or frozen bloodworms and brine shrimp to keep your fish in top condition.

Overfeeding your fish is a common mistake that can have some surprisingly serious consequences. Watch your fish eat; they should be able to finish their food in a minute or so.

Tank Maintenance

Maintaining a healthy neon tetra community tank takes a little regular maintenance.

Schedule an hour or so each week to perform regular water changes and tank maintenance. I recommend testing your water every week to monitor the build-up of nitrates and phosphates.

You can plan your maintenance schedule around the results of your tests and aim to keep your nitrate levels down to about 20 parts per million or less. You’ll also want to clean your glass and ornaments from time to time and rinse out your filter media when it begins to clog up.

However, there are some things you can do to minimize the amount of maintenance you need to do. Use these tips to keep your tank cleaner for longer:

• Avoid overstocking your tank. More fish means more food and more fish poop!
• Grow live plants
• Use high-quality filtration
• Avoid overfeeding
• Add clean-up crew animals like nerite snails and cherry shrimps

Where To Buy

Are you ready to get some new friends for your neon tetras? You should have no trouble tracking down the species in this list. Most local fish stores will stock these fish; just make sure to buy from stores that take great care of their animals.

More and more aquarists are buying their fish online these days. You can also consider ordering your fish from a trusted online retailer and having them delivered directly to your door!

Mark’s Pick: Corydoras catfish. They share the same water parameter range, stay on the bottom while neons stay mid-water, and are completely non-aggressive. A school of 8 neons with 6 corydoras in a planted 20-gallon is one of the most reliable, visually striking community combinations in freshwater.

FAQs

Who Is This Setup Right For?

Neon tetras were probably the first fish I ever kept seriously, and I’ve come back to them dozens of times since. The tanks where they look best are always the ones that were built around their needs first, soft water, plenty of plants, a large school, and peaceful companions that leave them alone.

Good Fit If:

• You want a peaceful planted community with soft, slightly acidic water (pH 6.0–7.0)
• You keep small, non-aggressive species that won’t stress or outcompete neons
• Your tank is mature, at least 3–4 months cycled, and water parameters are stable
• You’re stocking mid-water schooling fish with bottom-dwelling companions

Avoid If:

• You have cichlids, large barbs, or any fish that might view neons as snacks
• Your water is hard and alkaline, neons struggle outside their preferred parameters long-term
• You want to add them to a new tank, neons are sensitive to uncycled or unstable conditions
• You keep fin-nipping species, stressed neons hide, stop eating, and waste away

Final Thoughts

Use the tips in this guide to help you choose your next tank mates. Remember, choose peaceful, similar-size fish that enjoy the same water parameters as your neon tetras. Give them plenty of swimming space and keep their tank clean for a happy and healthy home aquarium!

What is your favorite neon tetra tank mate? Let us know in the comments below!

📘 Want to learn more? This article is part of our complete Freshwater Fish Guide. your ultimate resource for freshwater species, care tips, tank setup, and more.

One of the questions I get all the time from newer goldfish keepers is whether their fish actually sleep. usually after they notice their goldfish just sitting motionless at the bottom of the tank and start panicking. I’ve kept goldfish and seen this behavior more times than I can count. It looks alarming if you don’t know what you’re seeing, but once you understand what’s actually happening, it becomes one of those things you can actually use to gauge whether your tank environment is healthy.

Goldfish do sleep. they just don’t look like it. Without eyelids, they can’t close their eyes, which is why you’ll find them hovering motionless in a corner of the tank at night looking like they’re staring at nothing. After keeping and filming goldfish extensively over the years, I still find it funny how often this startles people who check on their tank late at night.

What’s worth knowing as a keeper is that goldfish need a consistent light/dark cycle to rest properly. Leaving your lights on 24/7 is one of those quiet stressors that’s easy to overlook but affects long-term health. Here’s exactly how goldfish sleep, what to look for, and how to make sure your setup supports it.

How Do Goldfish Sleep?

Goldfish might not tuck themselves under the covers each night, but they certainly do sleep! However, fish don’t sleep in the same way that you and I do. When goldfish sleep, their metabolism slows, and they become inactive. Research has shown that fish can enter deep sleep at night¹.

Until recently, fish were not thought to exhibit rapid eye movement or REM sleep like ourselves and other mammals. However, scientists have discovered that zebra danios enter a pretty similar state. We don’t know if danios or other fish like goldfish dream, but it’s certainly possible.

Goldfish sleep at the bottom of their tank to feel safer from predators. You might also find them sleeping between live plants or aquarium decorations where they can stay more still and feel secure.

Why Do They Sleep?

All that swimming and exploring in your aquarium certainly tires out your goldfish, so they need to rest regularly to stay healthy.

When

Goldfish don’t fall asleep like people each night, but they get most of their rest when it’s dark. That’s why providing your goldfish with a natural day and night cycle is important.

Running your aquarium lights all day and night can result in a sleep-deprived goldfish, so be sure to switch off the tank lights for at least twelve hours a day. Keeping your lights on for 6 to 8 hours a day is recommended because more than that can cause algae issues.

The best way to keep things regular in your tank is to set your aquarium lights on a timer. That way you won’t forget to switch the lights on or off.

Goldfish are sensitive to loud noises and sudden movements when they sleep at night. High noise levels will disturb your fish’s sleep schedule, so never put speakers or televisions next to your goldfish tank.

How Long?

Goldfish can sleep for short periods or for many hours at a time. Some goldfish nap during the day, while others sleep at night. Creating regular light and dark periods each day will allow your goldfish to develop its own natural sleeping pattern and get enough sleep.

Some goldfish owners report that their pets go to sleep in the same spot each night and are still there each morning. The important thing is to let your goldfish rest each day in a dark and quiet environment.

If your goldfish is not getting enough rest, it could cause stress and weaken its immune system in the long run.

Why Don’t Fish Close Their Eyes?

The simple answer to this common goldfish question is that fish don’t have eyelids. Eyelids are very useful for keeping our eyes moist and free of dust and other irritating particles. This isn’t a problem underwater, so goldfish don’t need to blink!

Is My Fish Sleeping Or Sick?

Many new goldfish owners are surprised to learn that their fish sleep, and it can be pretty worrying to see your pet sleeping motionless for long periods. However, you can rest assured that this behavior is completely normal.

However, goldfish can get sick with conditions like swim bladder disease from time to time, so it’s good to know if your goldfish is sleeping or showing signs of poor health.

Read on to learn what to look out for.

Signs Your Goldfish Is Sick

• Seeing your goldfish sleep upside down or leaning to one side could indicate swim bladder problems. Swim bladder disorder is a common illness among goldfish and other pet fish. This condition causes buoyancy issues which can make your fish sink, float, or swim erratically.
• Cloudy eyes, sores, or a white film over the body are often signs of a bacterial infection.
• Missing scales, white spots, and scratching against the substrate are common signs of parasites.
• Rapid breathing is a clear sign of stress, which can cause illness in your goldfish. Poor water quality, drastic water temperature changes, and disease can cause this common symptom. Rapid breathing can also result from low oxygen levels. Running an air pump and airstone can be helpful.

Signs Your Fish Are Sleeping

• Your goldfish is sleeping if it’s stationary at the bottom of the tank or hovering about an inch above the substrate. Most healthy goldfish rest at night when it’s dark, but you might find your goldfish sleeping any time.
• Sleeping goldfish often tilt their head downward slightly but keep their body upright.
• Your goldfish’s color might be a little dull when it is sleeping. This can help your fish hide from predators.
• Sleeping fish can breathe without swimming. They gulp water to maintain a constant flow through their gills.

What To Do If They Are Sick

Accurately diagnosing illnesses in freshwater fish can be tricky, but you can often find the cause of your fish’s health problems, and there’s a good chance that you can treat your pet at home.

Fish get sick when they are under stress, and stress is often caused by bad environmental conditions. What does that mean? Well, your fish need clean, healthy tank water at the right temperature.

• Test your water quality

Goldfish are pretty messy fish, so they need good filtration and a tank of at least 30 gallons to stay healthy. Your water quality can become dangerous if you don’t cycle your aquarium and perform regular water changes.

Your water should contain no traces of ammonia or nitrite. Nitrates can harm goldfish in high concentrations, so keep them below 40 ppm. A level of 20 ppm or less is ideal for long-term care.

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• Check your water temperature

Goldfish are coldwater fish that prefer a lower temperature range than most other fish. They should be kept in water temperatures between 68 and 74°F. Tropical fish tank water temperatures will harm your goldfish in the long run.

Aquarium heaters are adjustable, and they do show the water temperature. However, these readings can be pretty inaccurate. I recommend getting a thermometer so you can monitor your water temperature easily.

Digital thermometers with built-in alarms are great for this purpose. These handy machines let you know if the water gets too hot or cold for your goldfish.

• Other Parameters

Poor water quality with high ammonia levels and high water temperature are common causes of stress, but goldfish also have other preferred water parameters. Aim for the following readings:

• pH: 7 – 8.4
• gH: 100 – 300 ppm
• KH: 50 – 120 ppm

You can test these parameters with a master test kit. Any inconsistencies can cause stress on your goldfish and will need to be addressed as soon as possible.

Treating

Providing correct treatments for your goldfish can mean the differences between live and dead fish. Goldfish are susceptible to many illnesses, and it’s not always the fishkeeper’s fault when things go wrong.

Let’s look at some things you can do to help a sick goldfish.

• Move the sick fish into a quarantine tank

A quarantine tank is a small tank where you can administer treatments to your sick goldfish without affecting your other fish or aquatic animals. Your quarantine tank should hold at least a few gallons of water and have its own filter.

Test the water before moving your fish. If the water in your main tank is the problem, you’ll need to use fresh, dechlorinated water instead.

• Observe Your Goldfish

If your fish is not in obvious danger, observe it for a few days and give it a chance to recover. Starting an immediate treatment is not always necessary.

• Treatment

If your goldfish is in obvious distress or not improving, contact your vet and ask for advice.
There are some excellent fish medications available that you can administer yourself at home.

Condition-specific medicines are highly effective, but you can also treat several common fish illnesses with aquarium salt.

FAQs

Final Thoughts

So now you know, goldfish sleep too! Don’t worry if you find your fancy goldfish sleeping. They need their forty winks, too, even if it is technically impossible for them to get any shut-eye.

Have you seen your goldfish sleeping? Tell us about it in the comments below!

📘 Want to learn more? This article is part of our complete Freshwater Fish Guide. your ultimate resource for freshwater species, care tips, tank setup, and more.

References

• Seriously Fish — Species profiles and care data
• FishBase — Taxonomy and scientific data
• Practical Fishkeeping — Husbandry and care advice