Rainbow shark (Epalzeorhynchos frenatus)

Rainbow shark (lat. Epalzeorhynchos frenatus) is as popular as its very close relative – red-tailed black shark. As for their care, behavior and compatibility these fishes are very much alike, though there are some nuances and you will find out about them from our article.

Habitat in the wild

In the wild inhabits in the north of Thailand, Nakhon Sawan province, where they are caught in clean warm streams of Chao Phraya river headstreams.

According to data provided by different authors, hydro-chemical parameters of water where the fish was caught vary rather significantly: water hardness is from 3 to 12°, pH 6,5—7,8, This indicates that the fish has high adaptability.

This elongated greenish-gray fish with red fins look like they were born to swim fast. They look very fascinating among tank greenery and stones. Main food for this fish is fouling on snags, stones and plants.

With two pairs of short barbels the fish probes substrate and scrapes tiny organisms and algae from it. Its mouth is perfectly adapted for this purpose – it is turned downwards, since this is a bottom feeder.

The fish eagerly eats crustaceans, blood worms, small insects that fall into the water, though there isn’t much of such food in clean fast rivers where they live.


It is a bottom feeder that can be seen from its mouth shape. It has two large eyes on its small head, a scraping sucker mouth with two pairs of barbels and ceratoid filaments that cut algae and fouling from surfaces.

Body is elongated, flattened from sides with curved spine. The fish coloring varies from greenish and gray to black, the tail fin is red. Males have red fins and their anal fin has black edges.

There is also albinotic type of the fish (with red eyes and fins). It is recommended to keep them separately from green ones when they grow – is less competitive when it is young. Further, when the fish becomes adult, you can keep both species together.

Female is larger with fat pronounced abdomen.

In a tank the fish grows to become up to 6 in (15 cm) large. Fish is reproductive at the age of 11 — 12 month and its lifespan is about 5 years, but some of them may live much longer.

Difficulties in keeping

This fish is quite difficult in care and it is not recommend for beginners. Except requirement for tank conditions, the fish temper is another issue.

The fish is quarrelsome and territory dependent one. You should choose tank mates very carefully, since it may just kill the fish it doesn’t like.

Keeping in a tank

Scientific NameEpalzeorhynchos frenatus
Common NameRainbow shark, rainbow shark fish, ruby shark
Tank size30 gallons and more
DietOmnivorous bottom feeders
Temperature72°F- 78°F (22 to 26 °C)
Sizeup to 6 in (15 cm)

Just like any fish that inhabits in flowing waters, it requires clean water. Therefore, 20–25% of weekly water renew is a must as well as cleaning of tank substrate with a siphon from organic wastes. It is desirable to use canister filter that will create the flow in the tank resembling the fish natural habitat.

Considering fish size and activeness it should have a spacious tank – from 30 gallons of water and more. In the wild the fish inhabits in sand cays, therefore the best tank substrate for it is sand.

Though, in general, you can use any large grained substrate with smooth edges.

Despite the fact, that this fish is a bottom-dwelling one, it perfectly jumps and does it quite often. So, you should cover the tank.

Since fish spends all time on the bottom, it is important that it has enough shelters and quiet places, where it can rest. These can be flower pots, plastic and ceramic tubes, tank plants, snags etc. At that the fish will guard its territory both from other fishes and its relatives.

Some wooden elements provided with good illumination serve a perfect ground for algae to grow – this is additional natural food for the fish.

Tank plants are necessary and important, but keep in mind that rainbow shark can damage soft leaves and fresh sprouts.

Therefore, it’s better to choose tank plants with rough leaves or feed the fish with lots of vegetable food.

Hydro-chemical properties of tank water are less significant, since fish can successfully adapt to wide range of pH and dH values.

These are comfortable tank water parameters for keeping: water hardness 4 — 11, pH 6,0-7,5, 24 and 27 °C (75 and 81 °F).


In the wild feeds mainly on plant food – fouling, algae. But if you expect it to clean your tank, you are wrong. There are more efficient tank cleaners – otocinclus, bristlenose pleco.

In a tank rainbow shark becomes an omnivorous fish. It’ll eat all types of food that falls on the tank bottom. But for healthy living and good coloring the fish diet should consist mainly from plant food.

This may be artificial food for bottom feeders, various vegetables – cucumber, spinach, lettuce. Any type of food will do, as a rule the fish eats food leftovers after feeding its tankmates.

Compatibility and tank mates

This is a semi-aggressive and very territory dependent fish. The juveniles are more or less good-tempered, but as they grow they become more and more territory dependent. That’s why it is important to create as much as possible shelters in the tank.

Rainbow shark will find its place and will guard it even from fishes that are just swimming by. If there is enough space (which means that the tank is quite large), it guarantees you some peace and quiet in it.

But if the fish feels that the tank is crowded, almost all its tank mates will suffer.

Therefore, it goes without saying that rainbow shark can’t stand its kind. So, it’s better to have just one fish in the tank, otherwise fights are almost guaranteed.

As for the fish tank mates we can recommend such bottom-dwellers as bristlenose pleco and clown loach. Both are large enough and active, so they won’t let fish hurt them.

It’s better to keep fast fishes in middle water layer – like tiger barb, it won’t be disturbed much. Any kind of fish may inhabit in upper water layers, since fish gets there very seldom.

Gender differences: male vs female

Fish has almost no gender dimorphism. Only when the female has eggs you can tell it from a male fish, since it has rounded and fat abdomen.

As for albino species, it can be done earlier – the female fish abdomen becomes greenish – these are eggs growing inside her.


Unfortunately, E. frenatus is still bred only by means of gonadotropic injections. This is due to the fact, that rainbow shark is a river fish and it’s impossible to create conditions similar to those in a stream, including hydrological seasonal changes.

As it was mentioned above, rainbow shark can’t stand its kind. So, to keep a couple of fish you’ll need a very roomy tank, which is a problem for an amateur aquarist. This is the first reason why breeding in a tank at home is very seldom the case.

Another reason is, that it’s difficult to see between the male and female fish and to keep a school of fish is possible only in a spacious tank.

And the last obstacle is, that for successful spawning in a tank the fish requires stimulation with gonadotropic hormones.

Summarizing the above, we must say that breeding in a home aquarium is almost unreal thing. The species you see on sale were bred either in South-East Asia fish farms or caught in the wild.

About author: Sergey Schulz

Sergey is a founder and author of Meethepet.com. He’s been fond of aquarium husbandry since his early childhood. His favorite aquariums are biotopes (Amazon River), with Echinodorus and freshwater angelfish. However, through the years he’s had experience of keeping almost all types of freshwater fish and shrimps.