Costello Tetra Care Guide: Tank Setup, Diet, Tank Mates & More

Last Updated: March 26, 2026

There’s a small tetra swimming around in the hobby that most people have never heard of, and that’s a shame. The Costello tetra (Hemigrammus hyanuary) is one of those fish that looks fairly ordinary in a dealer tank under harsh fluorescent lighting. But bring a school home, settle them into a planted tank with a dark background, and suddenly that iridescent green-gold stripe starts catching light in a way that stops you in your tracks. It’s a subtle beauty, the kind of fish that gets better the longer you watch it.

The tetra for people who think neons are too loud.

If the name sounds unfamiliar, you may have seen this species listed as the January tetra or even confused with the green neon tetra. They’re different fish entirely, and I’ll clear that up below. What matters right now is that the Costello tetra is peaceful, easy to keep, and looks fantastic in the right setup. Let’s get into everything you need to know.

What Most Care Guides Get Wrong About the Costello Tetra

The costello tetra flies so far under the radar that most care guides just copy the same generic information back and forth. Here’s what they miss: costello tetras are more temperature-sensitive than most small tetras. They come from cooler blackwater streams and don’t do well when temps stay above 80°F for extended periods. I’ve seen keepers lose fish during summer heat waves because they assumed “it’s just a tetra, it’ll be fine.” The other issue is that guides recommend them for any community tank. In reality, costello tetras are quite timid. They need calm tank mates and plenty of cover, or they’ll spend all their time hiding behind the heater.

The Reality of Keeping Costello Tetra

Group size is not a suggestion. The minimum school size for costello tetra is not just a guideline. In small groups, these fish lose color, become stressed, and display abnormal behavior. A proper group of 6 to 8+ is where you start to see natural schooling behavior, full color expression, and the confidence that makes them worth keeping.

Tank mate selection requires thought. The costello tetra is not aggressive in the traditional sense, but it is assertive enough to cause problems with the wrong companions. Slow-moving, long-finned species are targets. Fast, short-finned fish of similar size are fine. Plan your community around this reality.

Hardy does not mean indestructible. The costello tetra tolerates a range of conditions, but it still needs basic care. Ammonia spikes, dramatic temperature swings, and neglected water changes will catch up to even the toughest species. The difference is margin of error, not immunity.

Store appearance is not home appearance. Fish in store tanks are stressed, crowded, and under inappropriate lighting. The costello tetra almost always looks better in a properly set up home aquarium than it does at the store. Dark substrate, live plants, and appropriate lighting bring out colors and behaviors you will never see in a retail environment.

Biggest Mistake New Owners Make

Keeping them with fish small enough to eat. This is a predator. It will eat anything it can fit in its mouth. If you stock smaller fish with a costello tetra, you are feeding it expensive live food.

Expert Take

Predatory fish are not for everyone, but the costello tetra is one of the more manageable predatory species in the hobby. If you understand the feeding requirements, the tank mate restrictions, and the space needs, it is a genuinely fascinating fish to keep.

Key Takeaways

• Minimum tank size is 15 gallons for a school of 6, though a 20-gallon or larger tank with 10+ fish really lets them shine
• Distinguished by a bright green-gold iridescent lateral stripe that runs from behind the eye to the tail, plus a dark spot at the base of the caudal fin
• Often confused with the green neon tetra (Paracheirodon simulans), but the Costello tetra is a completely different species in a different genus
• Peaceful, hardy, and adaptable, accepting a wide range of water parameters from slightly acidic to neutral
• Recently reclassified from Characidae to Acestrorhamphidae under the 2024 Melo et al. Phylogenetic revision

The Costello tetra is one of the most adaptable tetras available. It handles a wide range of water conditions, eats everything offered, and schools reliably in groups of 6+. It is the kind of fish that just works without demanding special attention. For keepers who want reliability over drama, this is the pick.

The Costello tetra does not need special treatment. It just needs a cycled tank and food. That is it.

Species Overview

Common Names	Costello tetra, January tetra, green neon tetra (misapplied)
Scientific Name	Hemigrammus hyanuary
Family	Acestrorhamphidae
Origin	Lake Hyanuary (Janauari) near Manaus, Amazon basin, Brazil
Temperament	Peaceful, schooling
Size	1.6 inches (4 cm)
Minimum Tank Size	15 gallons (57 liters)
Diet	Omnivore
Tank Level	Mid
Temperature	73-82°F (23-28°C)
pH	5.5-7.5
Hardness	2-12 dGH
Lifespan	3-5 years
Care Level	Easy to Moderate

Contents

• Key Takeaways
• Species Overview
• Classification
• Origin & Natural Habitat
• Appearance & Identification
• Average Size & Lifespan
• Care Guide
• Tank Mates
• Food & Diet
• Breeding & Reproduction
• Common Health Issues
• Common Mistakes to Avoid
• Where to Buy
• Frequently Asked Questions
• Closing Thoughts
• Recommended Video
• References
• Explore More Tetras

Classification

Order	Characiformes
Family	Acestrorhamphidae (reclassified from Characidae per Melo et al. 2024)
Subfamily	Pristellinae
Genus	Hemigrammus
Species	H. Hyanuary (Durbin, 1918)

The Costello tetra was first described by Marion Lee Durbin in 1918, based on specimens collected from Lake Hyanuary (also spelled Janauari) near Manaus, Brazil. For most of its taxonomic history, this species was placed in the family Characidae, the large catch-all family that housed most of the small tetras in the hobby.

That changed in 2024 when Melo et al. Published a comprehensive phylogenetic revision of the Characidae. Their molecular analysis resulted in the creation of several new families, and Hemigrammus was moved into the family Acestrorhamphidae, subfamily Pristellinae. You’ll still see most references list this fish under Characidae, and it may take years for the hobby and databases to fully catch up, but the reclassification is well-supported by the genetic data.

Origin & Natural Habitat

The Costello tetra’s type locality is Lake Hyanuary (Lago Janauari), a floodplain lake located just south of Manaus in the Brazilian state of Amazonas. This lake sits near the confluence of the Rio Negro and the Rio Solimoes, one of the most biodiverse freshwater regions on the planet. The species is also found in other tributaries and waterways of the greater Amazon basin, including portions of the Rio Negro drainage.

In its natural habitat, the Costello tetra inhabits slow-moving or still waters with dense vegetation. These are often blackwater or clearwater environments where tannin-stained water, fallen leaf litter, and submerged root structures provide cover and foraging opportunities. The water is typically soft and acidic, with temperatures that stay warm year-round due to the equatorial climate.

Understanding this origin helps explain the fish’s preferences in the aquarium. They do best with subdued lighting, plenty of plant cover, and soft, slightly acidic water. That said, most specimens in the hobby are commercially bred and adapt well to a broader range of conditions than their wild counterparts would tolerate.

Appearance & Identification

The signature feature of the Costello tetra is a brilliant green-gold iridescent lateral stripe that runs along the midline of the body from behind the gill plate to the caudal peduncle. Under aquarium lighting, this stripe shifts color depending on the viewing angle, sometimes appearing more green, other times flashing gold or even turquoise. It’s this stripe that occasionally leads to the fish being sold as a “green neon tetra,” though it bears only a superficial resemblance to the true green neon (Paracheirodon simulans).

At the base of the tail fin, you’ll notice a distinct dark spot (sometimes called a caudal spot), which is bordered by lighter coloration above and below. This is a reliable identification marker that separates the Costello tetra from several similarly shaped tetras. The upper half of the eye is a noticeable red-orange color, a trait it shares with the head-and-tail-light tetra and a few other Hemigrammus species. The body itself is a translucent silvery-olive, with the dorsal (upper) portion being darker and the belly area lighter.

Male vs. Female

Sexing Costello tetras takes a bit of practice. Females are typically rounder and deeper-bodied than males, especially when full of eggs. Males are slightly slimmer and more streamlined. The color differences between sexes are minimal, though males may display a slightly more intense iridescent stripe during spawning activity. Looking at the fish from above helps, as gravid females will be noticeably wider through the midsection.

Average Size & Lifespan

Costello tetras are a small species, reaching a maximum size of about 1.6 inches (4 cm) in total length. Most aquarium specimens settle in around 1.2 to 1.4 inches (3 to 3.5 cm). They won’t outgrow even a modest community tank.

With proper care, expect a lifespan of 3 to 5 years. Consistent water quality, a varied diet, and keeping them in appropriate school sizes are the biggest factors in reaching the upper end of that range. Stress from poor conditions or being kept in too-small groups will shorten their lives noticeably.

Care Guide

The Costello tetra falls into the easy-to-moderate care range. They’re not quite as bulletproof as neon tetras or black skirt tetras, but they’re far from demanding. The key is providing stable water conditions and a well-maintained tank. Here’s a breakdown of what they need.

Tank Size

A 15-gallon (57 liter) tank is the minimum for a school of 6 Costello tetras. If you want a larger school, and you really should for the best visual effect, step up to a 20-gallon long or 30-gallon tank. These are mid-water swimmers that appreciate horizontal swimming space, so a longer tank footprint is always preferable to a taller one. In a 20-gallon long with 10 or 12 Costello tetras, the schooling behavior becomes much more defined and the iridescent stripes create a really striking display.

Water Parameters

Temperature	73-82°F (23-28°C)
pH	5.5-7.5
Hardness	2-12 dGH
Ammonia/Nitrite	0 ppm
Nitrate	Below 20 ppm

While they naturally come from soft, acidic blackwater habitats, captive-bred Costello tetras adapt to a wider range of conditions. They do best in slightly acidic to neutral water, and soft water will bring out the most intense coloration. If your tap water runs a bit hard or alkaline, they’ll still do fine as long as you’re not pushing extreme parameters. Stability matters more than hitting a perfect number.

Tank Setup

A dark substrate, whether sand or fine gravel, will make the biggest visual difference with this species. That iridescent lateral stripe pops dramatically against a dark background compared to a light or bare-bottom setup. Add plenty of live plants, some driftwood, and a few pieces of leaf litter to replicate their natural habitat. Java fern, anubias, and Amazon swords all work well.

Floating plants are highly recommended. They diffuse overhead lighting and create the kind of dappled, shaded environment where Costello tetras feel most secure and show their best colors. Frogbit, water sprite, or red root floaters are all solid choices. Leave open swimming space in the middle and front of the tank so the school has room to cruise.

Filtration & Maintenance

Any standard aquarium filter rated for your tank size will work perfectly. Hang-on-back filters and sponge filters are both excellent choices. Since Costello tetras come from slow-moving or still water, keep the flow moderate to gentle. Strong current will stress them and force them to expend energy fighting the flow instead of schooling naturally.

Perform 25-30% water changes weekly. Consistent maintenance is the single most important factor in keeping any tetra healthy long-term. If you can keep nitrates under 20 ppm and avoid sudden parameter swings, you’ll rarely run into problems with this species.

Is the Costello Tetra Right for You?

The costello tetra is a specialist’s fish that rewards patience and the right conditions. Here’s who should consider them:

• You specialize in soft, acidic blackwater setups. That’s their natural element
• You want to keep a truly rare tetra that most hobbyists have never even heard of
• You can provide a calm, low-traffic tank environment with subdued lighting
• You’re patient. These fish take time to settle in and show their best
• You enjoy the challenge of keeping less common species healthy long-term
• Skip these if you want an active, front-of-tank display fish. Costello tetras are reserved by nature

Tank Mates

The Costello tetra is a genuinely peaceful fish with zero aggression or fin-nipping tendencies. It fits seamlessly into most community setups and won’t bother tank mates of any size, including small shrimp. The main thing to avoid is housing them with anything large or aggressive enough to view them as food.

Good Tank Mates

• Other tetras: Neon tetras, cardinal tetras, ember tetras, rummy nose tetras, glowlight tetras, pristella tetras
• Rasboras: Harlequin rasboras, chili rasboras, lambchop rasboras
• Corydoras catfish: Any species, including bronze, panda, pygmy, and julii corys
• Dwarf cichlids: Apistogramma species, ram cichlids, kribensis
• Gouramis: Honey gouramis, sparkling gouramis, pearl gouramis
• Livebearers: Guppies, endlers, platies
• Invertebrates: Amano shrimp, cherry shrimp, nerite snails, mystery snails
• Plecos and algae eaters: Bristlenose pleco, otocinclus

Tank Mates to Avoid

• Large cichlids: Oscars, Jack Dempseys, green terrors, and other predatory cichlids will eat them
• Aggressive species: Red devil cichlids, large aggressive barbs
• Large predatory fish: Arowana, pike cichlids, large catfish
• Fin nippers in large numbers: Tiger barbs may cause stress in mixed community setups

One nice pairing worth mentioning: Costello tetras look fantastic alongside cardinal tetras or green neon tetras. The different stripe colors (green-gold vs. Blue-red) complement each other beautifully, and all three species occupy similar water parameter preferences since they originate from the same general region of the Amazon.

Food & Diet

Costello tetras are unfussy omnivores that will accept just about any standard aquarium food. In the wild, they feed on small invertebrates, insect larvae, zooplankton, and plant matter. Replicating this varied diet in the aquarium is straightforward.

A high-quality flake food or micro pellet should form the staple of their diet. Supplement this with frozen or freeze-dried foods like brine shrimp, daphnia, bloodworms, and tubifex worms a few times per week. These protein-rich foods help maintain vibrant coloration and condition the fish for breeding. Live foods like baby brine shrimp or micro worms are also excellent if you have access to them.

Feed small amounts twice a day rather than one large feeding. Their mouths are small, so make sure any pellets or food items are appropriately sized. Crush flakes if needed. Remove any uneaten food after a few minutes to prevent water quality issues.

Breeding & Reproduction

Breeding Costello tetras is achievable but requires some preparation. Like most Hemigrammus species, they are egg scatterers that show no parental care. The adults will readily eat their own eggs and fry if given the opportunity, so a dedicated breeding setup is essential.

Breeding Difficulty

Moderate. They’re not the easiest tetras to breed, but they’re not the most difficult either. The main challenge is providing the right water conditions to trigger spawning and then keeping the eggs safe from the parents.

Spawning Tank Setup

Set up a separate breeding tank of 5 to 10 gallons. Keep the lighting dim, as the eggs are light-sensitive. Use a spawning mop or fine-leaved plants like java moss as a substrate for the eggs to fall into. A mesh or grid at the bottom of the tank works well too, sized so that eggs can fall through but adults cannot reach them.

Water Conditions for Breeding

Soft, acidic water is important for successful spawning. Aim for a pH of 5.5 to 6.5 and a hardness below 5 dGH. Temperature should be slightly warmer than their normal range, around 78-80°F (26-27°C). Using RO water mixed with a small amount of tap water or peat-filtered water helps achieve these soft, acidic conditions.

Conditioning & Spawning

Condition a breeding pair or small group with high-protein live and frozen foods for 1 to 2 weeks before introducing them to the breeding tank. Bloodworms, brine shrimp, and daphnia are all excellent conditioning foods. Well-conditioned females will appear noticeably rounder as they fill with eggs.

Introduce the pair to the breeding tank in the evening. Spawning typically occurs the following morning at first light. The female will scatter adhesive eggs among the plants or spawning mop while the male fertilizes them. A single spawning can produce 100 to 200 eggs.

Egg & Fry Care

Remove the adults immediately after spawning to prevent them from eating the eggs. The eggs are small and semi-transparent, and they typically hatch within 24 to 36 hours depending on temperature. The fry will be free-swimming about 3 to 4 days after hatching.

First foods for the fry should be infusoria or commercially available liquid fry food. After about a week, they’ll be large enough to accept freshly hatched baby brine shrimp. Growth is steady but not fast. Keep the rearing tank clean with small, frequent water changes and avoid sudden parameter swings during this delicate stage.

Common Health Issues

Costello tetras are reasonably hardy, but like all aquarium fish, they’re susceptible to a few common diseases. Most health problems in tetras is traced back to poor water quality or stress from inadequate schooling numbers.

Ich (White Spot Disease)

Ich is the most common disease affecting freshwater aquarium fish, and Costello tetras are no exception. Symptoms include small white spots on the body and fins, flashing (rubbing against objects), and clamped fins. Ich is triggered by temperature fluctuations or the introduction of new, unquarantined fish. Treatment involves raising the temperature to 82-86°F (28-30°C) over 24 hours and using a commercially available ich medication. Many experienced fishkeepers also add aquarium salt at 1 tablespoon per 5 gallons, though tetras are more sensitive to salt than some other freshwater fish, so use the lower end of recommended dosages.

Neon Tetra Disease

Despite the name, neon tetra disease can affect many small tetra species, including Costello tetras. It’s caused by the microsporidian parasite Pleistophora hyphessobryconis. Symptoms include loss of coloration, difficulty swimming, a curved spine, and a faded or patchy appearance to the lateral stripe. Unfortunately, there is no reliable cure for neon tetra disease. Affected fish should be removed and humanely euthanized to prevent the parasite from spreading to other fish in the tank.

Fin Rot

Fin rot is a bacterial infection that causes the fins to become ragged, frayed, or discolored. It’s almost always a secondary infection caused by poor water quality or physical damage. The first step in treatment is improving water quality through increased water changes. In mild cases, clean water alone is often enough for recovery. More advanced cases require antibiotic treatment with medications containing erythromycin or similar antibacterial compounds.

Common Mistakes to Avoid

• Keeping too few. A school of 3 or 4 is not enough. Costello tetras need a minimum group of 6, and they’re visibly more comfortable and active in groups of 10 or more.
• Too much light. Bright, unfiltered lighting washes out their coloration and makes them feel exposed. Use floating plants or dimmer lighting to bring out the best in this species.
• Skipping quarantine. New arrivals should always be quarantined for 2 to 4 weeks before adding them to your main display tank. This is especially important with wild-caught specimens.
• Confusing them with green neon tetras. They are different species with different care needs. Make sure you’re buying the right fish. Check for the caudal spot and red eye, which are absent in Paracheirodon simulans.
• Neglecting water changes. Consistent water quality is more important than hitting exact parameters. A regular schedule of 25-30% weekly water changes will prevent most health issues.
• Overly strong water flow. These fish come from still or slow-moving water. A powerful filter output pointed directly into the tank will stress them and disrupt their schooling behavior.

Where to Buy

The Costello tetra is not as widely available as neon tetras or cardinal tetras, but it is found through specialty online retailers. Two excellent sources to check are Flip Aquatics and Dan’s Fish. Both are reputable online fish stores that regularly stock less common tetra species and ship directly to your door.

You also find Costello tetras at well-stocked local fish stores, particularly those that specialize in South American species. Availability is seasonal, so if you don’t see them right away, ask your store to add them to their next order. When buying, look for active fish with bright, intact lateral stripes and clear eyes. Avoid any individuals with clamped fins, white spots, or faded coloration.

Expect to pay a bit more per fish than you would for common tetras. They’re typically priced in the $3 to $6 range per fish depending on the retailer and availability. As with all schooling fish, buy a group of at least 6 at once rather than adding a couple at a time.

Frequently Asked Questions

Is the Costello Tetra the same as the Green Neon Tetra?

No. This is one of the most common points of confusion in the hobby. The Costello tetra (Hemigrammus hyanuary) and the green neon tetra (Paracheirodon simulans) are completely different species belonging to different genera. While both display a greenish lateral stripe, the Costello tetra has a dark spot at the base of its tail and a red upper eye, neither of which the green neon tetra possesses. They also differ in body shape, with the Costello tetra being slightly more elongated.

How many Costello Tetras should I keep?

A minimum of 6, but 10 or more is strongly recommended. Larger schools show tighter schooling behavior, reduced stress levels, and more vibrant coloration. In a properly-sized tank, there’s no real downside to keeping a bigger group. A school of 12 to 15 in a 30-gallon planted tank is a stunning display.

Can Costello Tetras live with shrimp?

Yes. Costello tetras are safe with adult shrimp of all common species, including cherry shrimp, Amano shrimp, and other dwarf shrimp varieties. However, like most small fish, they may eat newborn shrimplets if they happen to encounter them. If you’re breeding shrimp, provide plenty of moss and dense plant cover where shrimplets can hide.

Why is it called the Costello Tetra?

The common name “Costello tetra” has been used in the hobby for decades, though its exact origin is unclear. The name “January tetra” is more straightforward, derived from its type locality of Lake Hyanuary (Janauari), which itself comes from the Portuguese word for January. You may see either common name used depending on the retailer or reference source.

Do Costello Tetras need a heater?

Yes, unless you live in a climate where your room temperature consistently stays between 73-82°F (23-28°C). For most fishkeepers, a reliable aquarium heater is essential to maintain stable temperatures within their preferred range. Temperature fluctuations are one of the primary triggers for ich and other stress-related illnesses in tetras.

Are Costello Tetras good for beginners?

They’re a solid choice for beginners who have cycled their tank and understand basic water maintenance. They’re more forgiving than some sensitive species like chocolate gouramis, but they’re not quite as indestructible as zebra danios or white clouds. If you can keep neon tetras alive and healthy, you can keep Costello tetras.

What It Is Actually Like Living With Costello Tetra

In a proper school, costello tetra display natural movement patterns that are genuinely engaging to watch. The fish interact with each other, establish subtle hierarchies, and move through the tank with purpose.

They occupy the middle water column during active hours, creating movement and visual interest in the zone where most fishkeepers want action.

Feeding time is when their personality comes out. They learn your routine quickly and will anticipate feeding before you even open the lid.

Their color and behavior improve over time as they settle into a stable environment. Fish that have been in the same tank for months look noticeably better than recently added stock.

They coexist peacefully with virtually every other appropriately-sized community fish. This compatibility makes tank planning straightforward.

How the Costello Tetra Compares to Similar Species

Costello Tetra vs. Green Neon Tetra

Green neon tetras share the costello’s preference for soft, acidic water and subdued lighting, but they’re far more widely available and better studied. Green neons are also more outgoing. They school beautifully in open water once settled. Costello tetras will stay closer to cover. Both are excellent blackwater species, but if you’re building your first soft water tank, green neons are the safer starting point. Costello tetras are for the keeper who’s already mastered the basics and wants something truly uncommon. Check out our Green Neon Tetra care guide for more details.

Costello Tetra vs. Ruby Tetra

Ruby tetras are another small, lesser-known species, but they’re more colorful and slightly bolder in the tank. Both species appreciate similar water conditions, but ruby tetras adapt to a wider range of parameters. If you’re choosing between the two for a soft water community, ruby tetras give you more color for less effort. Costello tetras are the better choice if rarity and uniqueness matter more to you than visual impact. Check out our Ruby Tetra care guide for more details.

Closing Thoughts

The Costello tetra is one of those hidden gems in the hobby that deserves a lot more attention than it gets. It’s peaceful, easy to feed, compatible with virtually any community setup, and offers a unique iridescent beauty that sets it apart from the more common tetras. That green-gold lateral stripe is genuinely eye-catching when you see it under the right lighting conditions, and a large school moving together through a planted aquascape is one of the more underrated sights in freshwater fishkeeping.

If you’ve been keeping tetras for a while and want to try something a little different from the usual neons and cardinals, give the Costello tetra a serious look. Set them up in a planted tank with subdued lighting, a dark substrate, and soft water, and you’ll quickly see why the fishkeepers who know this species will become lifelong fans.

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Recommended Video

Check out our tetra tier list video where we rank the most popular tetras in the hobby, including the Costello tetra:

References

• Melo, B.F, et al. (2024). Phylogenomics of Characidae. Molecular Phylogenetics and Evolution.
• Durbin, M.L. (1918). Original description of Hemigrammus hyanuary.
• Seriously Fish. Hemigrammus hyanuary species profile. seriouslyfish.com
• FishBase. Hemigrammus hyanuary. fishbase.org
• Planquette, P, Keith, P. & Le Bail, P.-Y. (1996). Atlas des poissons d’eau douce de Guyane. Tome 1.

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Explore More Tetras

The Costello Tetra is just one of dozens of tetra species we cover in our complete species directory. Whether you’re into rare Amazonian species or beginner-friendly community tetras, our guide has you covered.

Tetras: Complete A-Z Species Directory