The rainbow shark, or the Epalzeorhynchos frenatum, is not your typical image of a shark. It’s actually not even a shark and is more closely related to the minnow. They are very exquisitely colored and also go by the names ruby shark, red-finned shark/red fin shark, white fin shark, and many other names due to their coloring (more on that later).
They are a freshwater fish native to Southeast Asia and can be found mostly in river basins. They got their name thanks to their perky fins that give them the appearance of a shark. However, they are much smaller in size than ocean sharks and pose less danger to you. However, they do possess a little bit of the temperament of their larger counterparts and are considered a semi-aggressive fish.
They can range from needing easy to moderate care in the tank, so we would not suggest this species for beginners. It can’t be argued that they add a certain level of edge and attitude to your aquarium with their contrasting colors and intimidating name. Let’s take a deeper look at how to care for rainbow sharks.
Easy to moderate
6 inches maximum
Minimum Tank Size:
75°F - 80°F (24°C - 27°C)
pH 6.5-7.5, water hardness 5-11 dGH
Tank Mate Compatibility
Other freshwater fish
Table of Contents
Rainbow sharks can be easy to care for since they aren’t susceptible to many diseases. Their care level goes up due to their semi-aggressive nature. However, since they are a freshwater fish, they can be prone to some freshwater diseases such as bloat, ich, swim bladder and even constipation.
Bloat is quite easy to spot as it causes your rainbow sharks to balloon. It may not be too obvious, but bloating in a rainbow shark is similar to bloating in other animals. It’s caused by unpassed gasses and food or even fluids. Other than the obvious change in appearance, your fish may also act differently, such as not being as active as before.
Ich is a skin disease that can be seen across your rainbow shark’s scales and extend to their gills as well. Ich is present in the form of white spots across your rainbow shark. You may see your rainbow sharks start to exhibit odd behavior such as scraping themselves across surfaces. This action may even appear before the white spots, so monitor your rainbow shark closely.
Another issue is swim bladder, which is common among freshwater species. Awkward movement and the inability to swim in the direction they want to go in are common symptoms of swim bladder. You may also see your fish sinking to the bottom of the tank if they are used to being closer to the surface and odd behavior like being unable to keep their balance.
Finally, your rainbow shark may also suffer from constipation, but luckily this issue usually fixes itself. Similar to constipation in other animals, a lack of fiber can be a major contributor. Make sure your rainbow shark gets its fair share of veggies to balance out its diet. All in all, if you watch out for these issues, the rainbow shark is a resilient species that can handle a lot.
Temperament and Behavior
Will rainbow sharks kill other fish? Yes, and no. They are known to be semi-aggressive, and their ill tempers can be triggered if they feel like their territory is being impeded on. They are quite a territorial fish, which could lead to aggression. Other bottom-dwellers could bear the brunt of their feisty personalities. Also, because they tend to live near the bottom of your tank, the rainbow shark can have the same purpose of cleaner fish and crustaceans and eat algae.
Rainbow sharks are active swimmers and without enough space to accommodate them, they may turn their frustration to other fish and even be aggressive towards their own kind. Harmful behavior they exhibit may include fin biting, and head butting.
Do rainbow sharks like to hide? They do! This is why you need to make sure to decorate the tank with dense vegetation among other things. Also, to keep your rainbow shark safe and sound inside the tank, we would suggest an aquarium cover. This fish species have been known to jump, however uncommon, and to prevent them from leaping out of the tank, a cover can curb this behavior.
Rainbow sharks aren’t like the Great White or other sharks that come into mind. They are much smaller and are actually of the cyprinidae family. They have a long and sleek look to them with a flat stomach and upright fins that give them the appearance of a shark. They have many fins (7 in total), which gives them the appearance of a small arrow.
It’s difficult to sex the rainbow shark until they have matured. Females will be plumper and males will develop black lines on their tail fins. Much like other fish species, the rainbow shark males will be much brighter and vivid in coloration compared to the females.
How big do rainbow sharks get? Rainbow sharks can typically get to about 6 inches, but they may be a bit smaller in captivity. How fast do rainbow sharks grow? Rainbow sharks grow quite quickly and can get up to about 1-1.5 inches in the first few weeks and it will take them a few months at most to grow to their full size.
Typically, the rainbow shark is a dark gray color almost black with contrasting orange fins or red fins (we assume that’s where they get the ruby shark nickname). The gray/black coloration paired with red fins or orange fins is typical of the common rainbow shark, however, there are a few different kinds.
Albino rainbow shark
The albino rainbow shark is the complete opposite of the common rainbow shark. Instead of the dark body, the albino rainbow shark is all white (with pinkish undertones) and pale orange or red fins. Although the rarer and more coveted albino rainbow shark will have clear fins.
Glofish rainbow shark
The glofish rainbow shark is an amazing subspecies, although their story could spur controversy. There are no words to describe the majesty of these fish due to their fluorescent colors. They are the result of rainbow sharks having their genes spliced with jellyfish. Initially, there were only two colors available with cosmic names such as galaxy purple (slightly magenta) and sunburst orange. The best part? The coloring is completely natural!
However, glofish rainbow sharks are now available in 2 more colors, blue and green! Since they seem to glow, adding them to your tank with matching plant decoration could yield a neon tank that is even more impressive with a blacklight!
Typically, the rainbow shark can live anywhere from 5-8 years in captivity. Factors that can contribute to the lifespan of rainbow sharks include proper water conditions, maintenance, and monitoring for diseases.
Being omnivorous, the rainbow shark will require balanced meals of both meat and plants. Their diet in the wild is varied, and includes large amounts of plants, algae, insect larvae and other meat. They are quite easy to feed and aren’t picky. Since they are bottom-dwellers, you would need to feed them food that sinks to the bottom. Pellets are recommended over flake food because they sink better.
For algae, if they have tank mates then that part is pretty much taken care of. If you would like to add more to the diet, we suggest algae wafers or tablets. As for the carnivorous side of the rainbow shark, focus on brine shrimp and other crustaceans (live brine shrimp will be a treat), zooplankton and insect larvae. You can also supplement their diet with real blanched vegetables from your kitchen including lettuce and spinach.
Their meat diet has a direct impact on their coloration. Giving your rainbow sharks a steady flow of bloodworms will also make sure their coloration stands out. You can give the fry a varied diet right from when they are able to eat bigger food. This will make sure they grow to their full size and to be healthy adults.
They are small creatures that don’t need to eat too much. As a rule of thumb, only feed your rainbow sharks the amount they can consume in a span of 5 min. Clear out all the leftovers to ensure the purity of the water. Spread out their feeding to 2-3 times a day and that should be enough.
The rainbow shark is from the cyprinidae family, the same family as minnows and is native to freshwater basins in Southeast Asia.
As mentioned, the rainbow shark is used to tropical freshwater and is native to Southeast Asia. The best chance you have at cultivating a healthy tank of rainbow sharks is to mimic their natural environments. Plenty of oxygen and water flow is needed as well. No matter what species you decide to get (even the genetically enhanced glofish sharks) their needs for tank conditions will remain the same.
A lot of thick vegetation is also required. Not only do they lessen aggressive behavior by defining territory, but they are great places to hide in and explore for the active rainbow shark. Other decorations to add that can lessen the tension and make their lives more interesting would be driftwood, caves, and rocks.
As for the substrate, anything will do for rainbow sharks. It’s okay to cater to other species in the tank when it comes to the substrate or the plants you plan on keeping.
Some of the best plants for the rainbow shark are the following:
- Java Fern – They are a resilient and tough plant that can thrive in low light conditions. They don’t require a lot of care, fall within the aquarium specs a rainbow shark needs and can create beautiful aquascapes.
- Java Moss – Similar to its cousin, the java fern, the java moss is a tough plant that can span your entire tank.
- Hornwort – Also within the aquarium parameters is the hornwort, a near-indestructible plant that can be simply placed inside your tank.
They don’t have many needs in terms of lighting, so we would just suggest placing the aquarium in a space with access to adequate sunshine.
The rainbow shark is used to tropical waters and needs warmer temperatures between 75°F – 80°F (24°C – 27°C). Depending on where you live, a heater may not be necessary if these parameters in the aquarium can be maintained.
As for the water, keep it at pH 6.5-7.5, with water hardness at 5-11 dGH. Unfortunately, rainbow sharks are quite sensitive to water changes, which means you will need to change the water every week. Aim for about a quarter of the tanks water to filter out and replace.
Minimum Tank Size
Rainbow sharks are very active. They like to explore, hide and use the entirety of the tank. For this reason, even due to their small size, we would recommend a minimum tank size of at least 50 gallons. What’s also different about the rainbow shark is that because they don’t use much of the upper space, you need to make sure the tank is spacious length-wise.
Therefore, you need a longer tank to make sure they have enough space to swim. If your tank isn’t long and is only tall, your rainbow shark could still be lacking the swimming space needed and become aggressive. To lower the risk of aggression, a 60 gallon tank would be a good place to start if your tank isn’t elongated.
Maintenance and Care
To make sure nitrate levels are optimal, oxygen is sufficient and the water is clean, you will need to cycle out about 20-30% of the tanks water every week. Unfortunately, your rainbow sharks will need more tank cycling than other species. So do the math for how many gallons of water need to be cycled out in a 50-60 gallon tank.
Even if you think the tank looks clean, you may be surprised by how much debris is hidden among the plants and substrate. Once you jostle the aquarium around and move the decorations, you may be shocked by what you see. Due to this, we wouldn’t recommend eyeballing the water conditions and to actually test for it.
An easy way to cycle your 50-60 gallon tank is with a siphon. However, this could be very time-consuming if your tank is larger. This is another easier option, and that is with water change systems that will cycle and drain the water directly into your sink, minimizing the mess.
There are two ways you can deal with the inhabitants of the aquarium. You can either leave them in or take them out. If you decide to go with the siphon, leaving them in could be easier. However, you have to be careful and gentle not to disturb the rainbow shark tank too much.
If you go for the water change system, you need to be extra careful with the smaller fish. You do not want them to be siphoned out with the water and drained into your sink.
If you live in a colder country, investing in a submersible water heater is a good idea. They also would require a proper filter that can keep the water flow moderate and the water clean.
Suitable Tank Mates
As a bonus tip, you should always add more territorial fish into the tank last. If you plan on having a community aquarium, look into the tendencies, temperament and aggression levels of each species. If rainbow sharks are the only aggressive type, then be sure to add them last. This will ensure that they have less of a chance to claim territories and unleash aggression.
Adding a rainbow shark, who is known to be semi-aggressive to a peaceful community aquarium could disrupt the balance. If you think you can handle it, they are an excellent addition due to their appearance and tank cleaning benefits. We also mentioned before that other bottom-dwellers will most likely bear the brunt of their violent tendencies so you will want to avoid those types of fish (although there have been reports where they get along with minimal issues).
You also should refrain from adding any timid fish, aggressive fish, or ones of a smaller size. Another tendency that is prevalent in many species of fish is that these sharks may lash out at similar-looking fish. Look for aquarium mates that live in the middle or upper levels of the tank, are of a similar size, and can hold their own against the rainbow shark. That doesn’t mean they need to be aggressive, but they do have to be strong.
If you have a female rainbow shark, they are also generally nicer than the males and will exude less aggression. In a tank, we wouldn’t recommend more than 2 rainbow sharks at most. The typical aquarist generally goes for only one, so if you want an easier time in a community aquarium, go for a female.
You also need to consider the needs of all the inhabitants in the tank. If you have more than one species, chances are you will need a larger gallon tank. A rainbow shark tank with only one or two, the water parameters will be easier to grasp. It’s also a good idea to keep a separate tank handy (even if it’s not set up) just so you can separate fish that are being attacked, who are sick, for breeding purposes and cycling of the tank.
Rainbow sharks like a strong current, so you have to be sure that the tank mates you select can tolerate that. Suitable tank mates for the rainbow shark include:
It’s strongly advised for aquarists to have a rainbow shark tank with only one of the species. Rainbow sharks may not even play nice with one of its own. This is normal because even in the wild, the rainbow sharks tend to keep to themselves. You may feel that putting juveniles together in the aquarium turned out fine. That is because the territorial nature of rainbow sharks are not apparent until they mature.
What started out as a happy-go-lucky community aquarium for a pair of rainbow sharks could turn into a very aggressive environment – especially if you have other fish.
Keeping just one rainbow shark in the tank is easier once you know that they haven’t been successfully bred in the aquarium. Even when they are bred commercially for sale, the help of hormones have been utilized to increase the chances of success. Even with low chances of success, you can still try to breed rainbow sharks if you feel equipped.
In nature, red fin sharks breed during colder seasons, around October to November, but out of season spawning has been recorded as well. They are typical egg layers and the eggs are fertilized by the males after. It only takes about a week for the eggs to hatch.
Around when they hit sexual maturity (about 6 inches in length), you can attempt the breeding process. Since they are aggressive fish, you will need to monitor them well. If you start seeing aggressive behavior, you would need to separate them for a length of time before reintroducing them again. Even if you do manage to create the perfect aquarium environment for rainbow sharks to breed, you may still need to enlist the help of hormones to be successful.
The administration and calculation of at-home hormone dosage can be a bit tricky, but you can get a general idea of what is needed through here.
Make sure you have the following equipment ready for breeding:
- Aquarium (2, one for breeding and one for isolation)
- A pair of rainbow sharks
- Rocks and driftwood
- Live aquarium plants
- Submersible aquarium heater
- Aquarium thermometer
- Peat moss
- Brine shrimp eggs
- Commercial fry food
You will need to decorate a breeding tank specifically for this task. Judging from the size of the rainbow sharks, look into an aquarium that is at least 80 gallons. Make sure that your tank is properly decorated with plenty of caves, plants, driftwood etc., to give them plenty of places to hide and explore. They also need places like caves to be accessible to spawn if you happen to be successful in the breeding.
The water temperature doesn’t need to be changed too much and can remain in the normal range. As for the hardness and pH levels, those don’t need to change too much either. If you see the pH dipping slightly below normal, you can use the peat moss in our equipment list to balance it out.
There isn’t a lot of information about breeding rainbow sharks so they require a lot of monitoring. If you are successful, you need to keep a close eye on the parents after the spawning. Some species of fish will devour their own eggs, and since so little is known about breeding rainbow sharks, we aren’t sure if they will eat their young. If you see the risk of the parents consuming the eggs, then remove them immediately into a separate aquarium.
Once the fry has appeared, they will most likely feed on their yolk sacs. When they have fully consumed them, you will need to start feeding the baby fish. Try to start with algae and baby brine shrimp for a complete diet. Once the juvenile rainbow sharks have become used to these foods, you can later introduce pellets, flakes, blanched vegetables and more.
Are rainbow sharks suitable for your tank? If you are looking into starting a tank with just rainbow sharks, then the work is easy. All you need to do is be sure you have the proper-sized tank, the right substrate and water conditions to keep them well and healthy. If you have other fish in the aquarium, then you will have to consider not adding other fish after the addition of the rainbow sharks.
As a rule of thumb, rainbow sharks should be added last to any fish tank. This will minimize territorial tendencies and attacks. Complete the tank setup with plenty of places for your fish to explore and provide densely planted vegetation to mark territories.
Since the rainbow shark is a bottom-dwelling fish, the food you feed needs to reflect that fact and sink to the bottom. They aren’t picky eaters so as long as you balance their omnivorous diet, they will do well in captivity. These fish can get along well with slightly larger fish with strong personalities. They don’t need to be aggressive, but they should be able to handle an aggressive rainbow shark.
To be sure your fish are happy and well, we would suggest constant monitoring to rule out any common freshwater fish diseases such as ich and swim bladder. All in all, the rainbow shark is an amazing and exotic fish to add to your tank.