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The name, rainbow shark might trigger your inner human fear, but don’t worry! These adorable creatures, despite being omnivorous, pose no challenge to human beings.
Rainbow sharks or Ruby sharks are quirky and fun freshwater aquarium fish that are commonly found in the river basins of Thailand. Although popular, rainbow sharks are not common among novice keepers. Knowing this, I set up a complete beginner guide to give you an idea about this fish that usually prefers to stay alone.
In this article, I’ll walk you through rainbow shark care, its origin, natural habitat, and common diseases.
Let’s get started!
Brief Overview of Rainbow Sharks
|Scientific Name||Epalzeorhynchos frenatum|
|Common Names||Ruby shark, Red-finned shark, rainbow sharkminnow, green fringelip labeo, whitefin shark, and whitetail sharkminnow.|
|Origin||Mekong, Chao Phraya, Xe Bangfai, and Maeklong in Indochina|
|Activity||High/ very active|
|Lifespan||5 to 8 years (approx.)|
|Temperament||Aggressive / Dominant|
|Minimum Tank Size||Min. 50 gallons|
|Temperature Range||72 ° F to 80 °F|
|Water Hardness||5 to 11 dH|
|pH Range||6 – 8|
|Filtration/Water Flow||Fast (mimicking the river basins)|
|Difficulty to Breed||Difficult to breed|
|Compatibility||Moderate (get along with freshwater fish of the same size)|
|OK, for Planted Tanks?||Yes, especially for hard-leaved vegetation|
Origin and Natural Habitat
Rainbow shark (Epalzeorhynchos frenatum) is nothing like true sharks; they are freshwater fish, live peacefully with their kin, and feed on algae and plankton. However, they were named after the mighty sharks because of the upright dorsal fin that strikes a close resemblance to sharks while swimming.
The rainbow sharks originated from Southeast Asia, particularly Thailand, and are now commonly found in the freshwater basins of Mekong, Chao, Phraya, Xe Bangfai, and Maeklong.
Unfortunately, the habitat destruction in the wild resulted in the decreased population of rainbow sharks. However, in nature, they are bottom dwellers and mostly live in sandy substrates.
Even though rainbow fish is a peaceful breed, it gets territorial and might give a tough time to their smaller tank mates. Therefore, it’s a good idea to keep a few fish in the aquarium, that is closer to their own size. Also, rainbow sharks are a little high-maintenance and might pose a challenge to novice fish keepers.
So, choose wisely!
What Do They Look Like?
As I mentioned before, Rainbow sharks are commonly known as red-finned sharks, which earned their name because of the dorsal fin.
And if you see them swimming, you might mistake them for baby ocean sharks for once!
However, rainbow sharks are small and have elongated and slender backs with flat stomachs. Their fins, as the name suggests, are bright red with somewhat orangish hues. The bright red-orangish fins pop out against their dull grey bodies.
The dorsal fins of rainbow sharks comprise 11 branched rays with a prolonged fin tail. Like ocean sharks, the rainbow shark’s face is flat, but the snout is somewhat rounded along with an elongated body that tapers off at the tail.
What’s the difference between the males and females?
Before stating the differences here, I’d like to emphasize that male rainbow sharks are very dominant and aggressive toward their gender. Therefore, I always recommend keeping rainbow sharks carefully; one male in a tank is enough!
Coming back to the variations, there’s not much to name their gender, especially for juvenile rainbow sharks. To clearly reveal the gender, it’s always best to wait until the sharks grow completely and reach adulthood.
An adult rainbow shark has a thin body with bright red-colored fins and black lines on its tailfins. Comparatively, female rainbow sharks possess faded coloration with more pronounced bellies and the black, grey lines on the tailfins are absent in females.
How Big Can They Get?
At the time of hatching, the baby rainbow sharks are just mere blots that wander far and wide. However, it’s surprising that in a matter of a few days, they grow ½ inch to one-inch range.
After almost a month, a rainbow shark reaches its full potential size, which is approximately 6 inches in length. In some rare cases, the rainbow shark might grow as long as 8 inches. However, they only get that large in bigger tanks.
In any case, due to their size and active behavior, large aquarium tanks are a necessity for rainbow sharks.
Interestingly, both male and female red-tail sharks are almost the same size in all varieties, and they usually sexually mature when they are four inches in length.
How Long Do They Live?
Under favorable conditions, rainbow sharks have proven to live for approximately 5-8 years in captivity. However, few claims suggest they live longer in nature.
The lifespan of rainbow sharks depends on:
- Overall tank and water environment
- Diet rich in vegetable and protein matter
- Perfect sandy substrate for bottom-dwelling
Temperament and Activity Level
One thing that I genuinely love about the Rainbow shark breed is its agile and lively nature (video source).
Also, since they are bottom dwellers, they enjoy their time in the water grazing for food.
Therefore, many aquarists discourage tanks or aquariums for the rainbow shark as the confined space might trigger their aggressive side. As a result, they might attack smaller sharks and ultimately kill them.
Nonetheless, if you want to keep a group in home aquariums, make sure to install a large tank.
Mature ones are territorial
Juvenile rainbow sharks are social and get along with other fish pretty well.
But as soon as they reach adulthood, they become standoffish and solitary, asserting dominance in the presence of other fish.
To cater to this, I advise making tunnels, caves, and crevices for hiding. Also, it’s advisable to plant dense and healthy vegetation for the well-being of other fish and thriving a healthy community that involves fewer accidents.
What are Good Tank Mates for Them?
Well, if you ask me, I’d say, no mates are always better!
You might argue that they get along with true loaches and plecos really well.
Yes, I agree!
But in the wild only. In captivity, the rainbow sharks are quite aggressive and territorial. And like I mentioned before, they are bottom-dwellers; they don’t enjoy the company of other scavengers.
And this brings me to the conclusion that bottom dwelling tank mates should always be avoided for Rainbow sharks.
However, if you’re still adamant, I advise you to introduce your red-fin shark to a pre-occupied tank with only a few fish to reduce the likeliness of harassment.
Red-fin sharks are compatible with upper and middle tank dwellers, including.
Also, while introducing rainbow sharks to their tank mates, be wary of their size and personality so that they could defend themselves.
Least Compatible Tank Mates
The worst tank mates for Rainbow sharks are shy and small fish, which are easily dominated.
Also, avoid bottom dwellers, very large, and aggressive tank mates including.
- Red-tailed shark
- Bala sharks
- Red Devil Cichlids
- Green Terror Cichlids
What do they eat?
The fact that rainbow sharks are omnivorous makes them voracious eaters. Also, they are not finicky and enjoy plants and prey.
The feeding habits in their native habitat rely on decaying plants, plankton, algae, insects, larvae, worms, and much more.
However, in captivity, since we target good coloration and a healthy lifespan, it’s best to include high-quality vegetable and protein matter.
For exquisite coloration and luster, I recommend feeding plants to the fish, such as lettuce, cucumber, cabbage, etc.
Also, they are bottom-dwellers, so make sure you get sinking pellets so they don’t miss out on some good nutritional diet.
Juveniles should munch on a protein-rich diet (brine shrimp, worms, and live food) to remain healthy and become brighter and stronger as they age.
However, since rainbow sharks are scavengers, they sometimes might overeat, which results in some illnesses. Therefore, it’s best to start feeding once a day to understand their pattern and adjust the diet accordingly.
Normally 2 feeding sessions a day comprising 5 minutes of feeding works the best for rainbow sharks.
Below is the list of recommended food you should incorporate into the diet of your rainbow shark.
- Insect larvae
- Algae (tablets/wafers)
- Tubifex Worms
- Brine Shrimp
- Vegetables (peas, cucumber, zucchini, lettuce, and spinach)
The most common and popular variation of Rainbow sharks is the Albino variant.
The Albino rainbow shark possesses white abdomens with bright red eyes and fins that make them stand out in the tank. Though the variety is extremely rare, it is fondly loved by aquarists.
Albinos are very active, bottom-dwellers that feed on biofilm, plankton, and other organisms in the freshwater. Juvenile Albinos are sociable and amicable. However, as they age, they become more distant and aloof. Hence, they don’t get along with fish of their own kind including Flying Foxes, and Siamese bottom feeders.
If you’re planning on keeping your Albinos in a small tank, think again!
Albino rainbow shark is known to be a very active jumper, so it demands large tanks with ample water flow and decent filtration. I also recommend installing protective aquarium lids, just so you don’t have to deal with accidents.
As long as the diet of Albinos is considered, get your fresh veggies ready, as Zucchini, Cucumber, and other high-quality vegetable and protein matter (brine shrimps, frozen bloodworms) are ideal for Albino Rainbow Sharks.
Personally, I would recommend Albino Rainbow shark to experienced fish keepers because:
- Slightly aggressive
Let me be very honest here.
If you’re raising rainbow sharks for the purpose of breeding, it’s time to move on!
That’s because the chances of breeding rainbow sharks, especially in captivity, are close to none.
Firstly, in their juvenile years, it’s impossible to distinguish between males and females. Secondly, rainbow sharks are so dominant and aggressive that they barely allow other fish to share the tank.
Therefore, there are few successful results of breeding rainbow sharks in aquariums (video source).
In nature, it’s a different story.
Rainbow sharks or Ruby sharks, like mentioned earlier, reach their sexual maturity as soon as they are 4 inches. The females lay eggs and males fertilize them later.
The ideal breeding months of Rainbow sharks are October and November. Thereafter the male fertilizes the eggs and the eggs are then transferred to a separate tank until the fry appears after a week.
The fry depends on high-quality protein so that they develop vibrant red fins and a healthy luster.
Luckily, you don’t need to care much about the rainbow shark as it enjoys its own company and eats whatever is accessible to them.
However, if you are someone who believes in the healthy nurturing of their pet fish, the tank size, balanced, and water quality of the aquarium should be your top priority.
While keeping the rainbow shark, know that we don’t start small here.
That being said, 50 gallons tank size is the bare minimum, that too for one rainbow shark.
If you’re planning on keeping multiple rainbow sharks, be sure to provide substantial tank space.
Also, the length of your tank should at least be four feet long and 18 inches wide, considering a single fish.
Since rainbow shark is an active jumper and avid swimmer, it’s best to keep the tank big and wide so that your adorable red-finned pets can get the most of their lives.
An interesting factor that keeps most aquarists from raising rainbow sharks is their fondness for their natural environment.
It’s almost impossible to recreate the natural conditions for rainbow sharks to reduce their aggression and dominance.
However, all we can do is try!
Rainbow sharks originally come from Southeast Asia’s freshwater basins where the water temperature ranges between 72°F to 82°F.
Therefore, the optimal water temperature for the rainbow shark falls somewhere between 77°F.
So, I suggest maintaining the water temperatures of your tank between 72°F to 82°F with the help of a premium heater that sets the temperature effectively.
Also, in the wild, these sharks enjoy river water that flows at a higher speed.
Therefore, maintain the water movement of the tank between moderate or fast to mimic their natural habitat.
Water pH and Hardness
Water pH and hardness are essential to maintain for keeping rainbow sharks calm and stress-free.
The ideal pH level ranges between 6 to 8 pH while the water hardness should be no less or more than 5 to 11 dH.
Substrate and Water Flow
Being a freshwater fish, the rainbow shark loves sandy bases. Also, many aquarists believe that’s a plus point because the sand is easy to clean and seldom collects food and other fish food waste that may be harmful to your fish.
Natural sand is excellent for bottom feeder fish to forage around in.
Besides sand, you may opt for round gravels that are not too edgy or sharp to avoid potential injuries.
Additionally, as I mentioned before, the water flow should also be maintained to entertain your rainbow shark. I recommend installing small jets and air-stones to control the constant water pressure and flow.
If your tank houses more than one rainbow shark and is over 125 gallons, you can make use of controllable wavemakers, including EcoTech, IceCap, and several others.
If you want to keep Rainbow sharks as your pet, I cannot stop stressing enough about recreating their natural habitat as they get quite upset in plain captivity.
The river basins in Thailand are filled with hiding places and natural vegetation. Therefore, you should consider freshening up the aquarium experience.
The sandy substrates help their scales from damaging when they are scavenging at the bottom and the hiding places give them plenty of space to spend their time in solitude.
I recommend setting up a tank with driftwood, boulders and pebbles, caves, and rock formation with lots of other decorations to keep your red-finned shark busy and happy.
Aquatic plants with hard foilage are also an excellent option to change their game. Since they are omnivorous, they like to munch on plants and green algae. Therefore, aquarists suggest keeping hard-leaved plants in the aquariums.
Also, the plants and decorations reduce the chances of conflicts between the different fishes. Nevertheless, if your tank houses just one rainbow shark, the decors and plantations are pretty straightforward.
Furthermore, it helps them to have a peaceful corner for themselves to feel safe and secure. When they feel unharmed, they are pleasant and lively.
The best plants for rainbow sharks are.
- Java Fern
- Lemon Bacopa
- Amazon sword
If you ask me, I’d say lighting isn’t a requirement for rainbow sharks. However, it’s always best to follow a natural day and night cycle to offer them their natural lifestyle.
Also, stronger illumination help algae to develop in your tank, which allows easier grazing for your rainbow minnow.
However, sometimes the bright lightings might get a little overwhelming for your sharks. Therefore, I recommend installing LED lights that are more economical and programmable.
The rainbow shark demands exceptional water quality, tank size, and proper sanitization and filtration.
Rainbow sharks cannot stand low oxygen levels and toxins such as nitrates, nitrite, and Ammonia. So, a filter would be essential for raising a healthy rainbow shark.
For filters, I recommend investing in a canister filter better than the HOB.
That’s because the ideal range of rainbow shark filters should be 360GPH and above, and the canister filter will provide just that.
If you have small sharks in your aquarium tank, fret not!
Canister filters can be easily adjusted and provide the perfect volume for your tank.
In terms of diseases and other illnesses, rainbow sharks are pretty hardy. But like any other freshwater fish species, they sometimes catch illnesses that are common and can easily be treated.
Some of the diseases are discussed as under.
Swim Bladder Disease
If you notice your rainbow fish swimming queerly, you might mistake it with the fun behavior.
However, it’s much more than that!
The swim bladder disease is a serious medical condition when a fish cannot swim properly and have difficulty controlling their ability to swim or float.
- Standing on the head
- Swimming upside down
- Distended belly
- Loss of appetite
- Curved back
- Floating on the sides
The major cause of swim bladder disease is the compression or squeezing of the swim bladder by overeating, gulping air, or constipation.
Some other causes also include.
- Bacterial infection
- Egg bound, in females
- Fatty liver tissues
If you have spent much time looking after aquarium fish, you might have noticed stingy feces, usually hanging from the fish.
That’s the major symptom of constipation.
When that occurs, wait for a few days and it should be gone on its own. But in severe cases, feeding a balanced diet that includes peas, brine shrimp along salt baths should help alleviate the symptoms.
- Stingy and hanging feces
- Lack of fiber
Will they eat other fish?
In wild, no!
However, things rainbow sharks are semi-aggressive when they are kept in captivity and might attack other small fish or fish of their own kind.
Therefore, it’s best to stick with one or a maximum of two fish, provided that there is ample space in the tank and other decors.
Which fish can live with them?
You can keep fish that are upper and middle-tank dwellers and possess a powerful personality that can defend back.
- Indian Loach
- Clown Loach
How aggressive are they?
Albino Rainbow sharks are of the same kind as normal rainbow sharks. Therefore, they show aggression and dominance towards other smaller fish and fish that are too shy to fight back.
How big of a tank do they need?
Rainbow sharks need ample space and time to adjust to their tanks. Therefore, keeping the tank as big as at least 50 gallons would suffice the needs of your rainbow shark.
That being said, the tank size should also increase when the number of fish increases.
Are they aggressive?
Yes, rainbow shark (Ruby shark) is pretty aggressive and shows some serious behavioral problems. Therefore, a novice fish hobbyist can hardly keep up with them.
Not only they are aggressive but demanding as well. The tank size, the decors, the vegetation, pH, and Oxygen levels should fall under the recommended range to keep your rainbow shark happy.
Rainbow shark is a beautiful freshwater aquarium fish that adds grace to your home. However, if you cannot afford a bigger tank, I suggest you keep looking for other better and smaller alternatives like nano fish.
One thing that I would strongly advise is recreating the natural environment within the tank with the recommended decors and aquascape.
Also, a happy rainbow shark is mellow and decent. So, make sure to gear up all the essentials before you bring one home.
Mark is the founder of Aquarium Store Depot. He started in the aquarium hobby at the age of 11 and along the way worked at local fish stores. He has kept freshwater tanks, ponds, and reef tanks for over 25 years. His site was created to share his knowledge and unique teaching style on a larger scale. He has worked on making aquarium and pond keeping approachable. Mark has been featured in two books about aquarium keeping – both best sellers on Amazon. Each year, he continues to help his readers and clients with knowledge, professional builds, and troubleshooting.