Rainbow Shark 101: Care Guide, Tank Size, Food & Tank Mates

Rainbow sharks are a fun and unique fish that can be very rewarding to keep.

However, there are some things you need to know before you think about getting one for your tank.

In fact, the rainbow shark might be one of the most misunderstood fish in the aquarium world (especially by beginners). That’s why we thought it was important to set the record straight and lay out the facts.

In this guide we go over their origin, behavior, appearance, and how to care for them.

By the time you’re done reading this, you’ll have a solid understanding of rainbow sharks and what they need to thrive in a tank.

Let’s get started!

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What Are Rainbow Sharks?

Sometimes referred to as a red-finned or ruby shark, the rainbow shark is native to Southeast Asia. They are not a saltwater fish but instead, thrive in freshwater. In particular, they live in the rivers of Myanmar, Thailand, Laos, and Malaysia.

They prefer rivers with sandy bottoms and plenty of plankton. However, they are also known to migrate into floodplains during periods of heavy rain or flooding.

Rainbow sharks are not true sharks. Instead, they are given their name because they have a shark-like appearance due to their dorsal fin on top.

True sharks also belong to the Chondrichtheyes family, but rainbow sharks are part of the Cyprinidae family, which is the same family as minnows. They belong to the cypriniformes order and are classified as Epalzeorhynchos frenatum.

Author Note: With that being said, it’s common to classify this species as a freshwater shark that you can keep in a variety of fish tanks.

This species was once abundant in the waters of Southeast Asia, but have dwindled in numbers in recent years. Scientists believe that the damming of certain rivers such as the lower Xe Bangfai has led to fewer rainbow sharks in recent years.

River dams may decrease floodplains and may therefore interfere with the ruby shark’s breeding patterns. The aquatic trade has little effect on their numbers in the wild as just about all commercially-available rainbow sharks originate from farms in Thailand.


Of course, rainbow sharks are well known for their red fins, which is primarily what gives them their name. Aside from being red, their fins may sometimes take on an orange hue as well. 

Ruby shark at bottom of rocky tank

Their colorful fins stand out even more against their gray or black bodies, which tend to be very long and slender. Some rainbow sharks will also have a dark blue body, although this is somewhat less common.

These fish have dorsal fins that may consist of up to 11 branched rays, along with a forked tail fin.

The rainbow shark’s face is rather flat, with a somewhat rounded snout in front. There are two eyes, one on either side of the head that often appear to be sunken. The rest of the rainbow shark’s body is rounded near the head and back and then tapers off as it nears the tail.

There is some color variations between males and females. For example, males tend to have brighter red or orange fins than females do.

Males will also have thin gray lines on their tail fins, while females will not have any lines. 

Female rainbow sharks also tend to be thicker and have more rounded bellies. These become apparent as the fish mature as there is basically no difference between juvenile male and female rainbow sharks.

You’ll have to wait until the fish are sexually mature to distinguish males from females.

The Albino Rainbow Shark

There is an albino version of the rainbow shark. This fish has the same red fins as the rainbow shark but has a white body rather than blue or black markings.

Albino rainbow shark

Sometimes, the body of an albino rainbow shark will take on a light pink or yellow hue as well. The light-colored body contrasted with its brilliant fins gives the albino rainbow shark a unique, yet highly sought after appearance.

General Behavior and Temperament

In their natural habitat, rainbow sharks are rather passive and do not really prey on other fish or aquatic animals.

That doesn’t hold true in captivity however. 

When placed in an aquarium, rainbow sharks are then considered a semi-aggressive fish. Semi-aggressive fish are those that may attack other fish if the circumstances are right.

Rainbow sharks are somewhat territorial and are therefore more likely to attack if their space is threatened. This is the biggest reason why having a large enough tank is so important (more on that later).

When given the right amount of space, rainbow sharks will typically get along well with other freshwater fish. With that being said, there are certain fish that should not be placed in a tank along with rainbow fish.

Some rainbow sharks are also naturally more aggressive than others and may become more territorial with age. As such, you should always use caution when introducing your rainbow shark to other fish.

Due to their territorial nature, these fish are not recommended for beginners.

Average Rainbow Shark Size

The size of a rainbow shark at full maturity is typically no longer than 6 inches long. There are some that have grown to be as long as 8 inches in length, but those are an exception.

This size holds true for normal rainbow sharks as well as the albino varieties. Both males and females tend to be about the same size in length.

The main difference between males and females when it comes to their shape and size is that males are a little more slender.

When rainbow sharks hatch from eggs, they are not much more than mere specks. From there, they grow rather rapidly.

Between two and four weeks of age, the fish will have grown to somewhere in the ½ inch to one-inch range. It can take several weeks or even months for them to reach their full size.

A red-finned shark is considered sexually mature when it is at least four inches long, but may nonetheless continue to grow after that.


The average lifespan of a rainbow shark is between four and six years long, although some have been known to live for as long as eight years.

That’s much longer than other aquarium fish such as bettas, which may only live for about two years. However, it is much less than goldfish, which can have a lifespan of up to twenty years.

The quality of water in your tank is a key factor in how long your rainbow shark will live. If your water supply has high levels of chlorine or chloramine, you may need to treat it with Amquel or sodium thiosulfate.

Rainbow Shark Care

There are a few things you need to consider when it comes to caring for rainbow sharks. Overall they are tough little guys and don’t need to be babied, but that’s assuming you take care of their essential needs.

Below we highlight the main areas that you need to focus on when it comes to rainbow shark care.

If you stick to these guidelines you’ll be well on your way to ensuring that your rainbow shark lives a happy and healthy life.

Tank Size

The ideal rainbow shark tank size is 50 gallons (at minimum). This will obviously increase depending on the number of other fish you keep in your tank, but in our opinion, you shouldn’t consider anything smaller.

To go smaller is not fair to them or any other fish you plan on keeping in the same tank. Rainbow sharks need space to thrive and feel like they’re in control of their territory/area of the tank.

Rainbow shark

The tank itself should be at least four feet long and 18 inches wide if you are only keeping one fish. 

This will give your rainbow shark plenty of room to swim around in. If they don’t have enough horizontal space they’re more likely to become aggressive and feel cramped.

This tank size will also leave you enough space to add caves, rocks, and other objects for it to hide in and explore.

Of course, you should leave at least a few inches of space on top to allow for oxygen in the tank. Keep this space requirement in mind when calculating how many gallons of water your tank will hold. 

When in doubt, always switch to a bigger tank. Although a 50 gallon tank is recommended, you’ll have even better luck if you go with a 55 gallon or larger.

These fish tend to feel cooped up unless they have ample space, and are more likely to become aggressive when placed in smaller tanks. Always ensure your tank meets the space requirements in order to maintain a safe, healthy environment for your rainbow sharks and other fish.

Some people may wish to breed rainbow sharks, which can be pretty tricky. If you want to try your hand at mating red-finned sharks, you’ll definitely need a larger tank.

A tank size of at least 75 gallons is recommended for a mating pair of sexually mature rainbow sharks. This will provide enough room for water, hiding spaces, and some gravel for the female to deposit her eggs into.

Ideal Tank Mates For Rainbow Sharks

In their natural habitat, rainbow shark dwell near the bottom of rivers.

This means they also tend to dwell near the bottom of their tanks, and may also stake claim on caves, tunnels, or any hiding area down there.

Accordingly, you should avoid placing rainbow sharks with tank mates that tend to dwell on the bottom as well.

A shortlist of fish that make terrible rainbow shark tank mates are:

Instead, choose species that dwell near the middle or top of the aquarium, and have the ability to defend themselves if needed. A few examples of good rainbow shark tank mates are:

  • Rasboras
  • Danios
  • Gouramis
  • Loaches (this can be dicey if you have a particularly aggressive rainbow shark but it’s usually fine)
  • Rainbowfish

Schooling fish normally do not due well with rainbow fish because most of them also like to swim near the bottom. One exception are barbs, which have been known to cohabitate peacefully with rainbow sharks.

Due to their semi-aggressive nature, there is always some risk anytime you place other fish in a tank with rainbow sharks.

To counteract this, place other fish in your aquarium first and introduce your rainbow shark last. This makes it less likely that your shark will see the aquarium as his territory.

Also, give plenty of plants or other materials for fish to hide behind. This will keep everyone a little safer, and a rainbow sharks is far less likely to attack if they are unable to see other fish.

You are also less likely to notice aggression if the other fish are about the same size or bigger than your rainbow shark.

That’s because some rainbow sharks sometimes try to assert their dominance over smaller fish, but are less likely to do so with ones their own size (little bullies).

Rainbow sharks may even become aggressive toward other fish that have a similar appearance. This is one reason why red tailed shark should never be placed in the same aquarium.

Rainbow sharks may sometimes become aggressive with one another as well. This may be because one fish is trying to assert dominance over the others.

For this reason, you may want to include at least five rainbow sharks if you plan to own multiple ones. That number provides the dominant rainbow shark with more fish to pick on so that no one creature is getting picked on more than it should.

When breeding red-finned sharks, watch the pair carefully to see if one fish is trying to assert dominance over the other. If this happens, you will need to remove one of the fish and then look for a different pair to breed.

What Do Rainbow Sharks Eat?

In their natural environment, rainbow sharks are mostly omnivores that eat a lot of algae, larvae, and bits of meat.

In an aquarium, they will also eat any algae that naturally forms at the bottom of your tank. You can also give them algae in tablet, flake, or wafer form if there isn’t enough inside your tank for them to dine on.

Rainbow shark with blue body eating

While algae is a common part of the rainbow shark’s diet, they require a balanced diet.

Some great food choices that they’ll enjoy and help them stay healthy are:

  • Frozen bloodworms
  • Fish granules
  • Brinefish
  • Insect larvae
  • Tubifex worms
  • Crustaceans
  • Aquatic insects

For a little variety, you may add bits of chopped cucumber, raw peas, or pieces of spinach as well.

Ideally, you should feed your fish a variety of plant and animal material. Perform feedings at regular intervals approximately two or three times each day.

Take care not to overfeed your rainbow shark. Give only what your fish can consume during a single meal, and do not try to compensate for skipped meals by feeding more.

It’s especially important to pay attention to the ruby shark’s diet while it’s still a juvenile. Feed young sharks a variety of vegetation to ensure proper growth and color.

Fish that do not receive adequate vegetation while young may have their growth stunted and fins that aren’t as brightly colored as they should be.

Water Details

Maintaining the right pH levels is very important if you want the best for your fish. Rainbow sharks do best in water that is between 6.5 and 7.5 pH.

Before introducing them to a new tank environment, prepare your water and allow it to cycle for at least two weeks so that it has time to stabilize. Use a heater to bring your water temperature to between 72 and 79 degrees Fahrenheit.

Upon bringing your rainbow shark home, place it immediately into your tank using a net. You don’t want it to spend more inside its transport bag than it has to.

Doing this will prevent shock and provide your rainbow shark with the best possible environment in which it can thrive.

What’s Next?

Now that you have a better understanding of rainbow sharks and how to care for them, it’s on you to decide if you want to give it a shot.

As we covered above, they need specific conditions in order to thrive and coexist with other fish. They aren’t the highest-maintenance fish out there, but they aren’t your run of the mill goldfish either!

Despite the extra work, we believe that rainbow sharks are some of the most rewarding fish you can keep. They look great, are a ton of fun to watch, and are a great way to take your fishkeeping journey to the next level.

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