Rainbow Shark

1 Species Overview

The Rainbow Shark comes from Thailand and is a mid-to-large-sized tropical fish, reaching about 14 cm as an adult. It is relatively easy to keep and is not demanding about water quality. It is an egg-laying fish that guards its eggs and generally does not eat them.

Common name: Rainbow Shark. Alias: Red-Fin Shark. English name: Labeo frenatus / Rainbow Shark. Scientific name: Epalzeorhynchus frenatus. Origin/distribution: Thailand, Malaysia, Sumatra and Borneo (Indonesia). Adult length: 12.0–15.0 cm. Temperament: aggressive. Suitable temperature: 23–29°C. pH: 6.0–7.5. Hardness (dGH): 4–12°N. Active water layer: bottom. Breeding: egg-laying (oviparous).

2 Morphological Characteristics

The Rainbow Shark is an easy-to-keep tropical fish of mid-to-large build, reaching up to about 12 cm. The body is spindle-shaped and can be 5–6 cm deep.

Its body shape resembles that of the Red-tailed Black Shark and it grows to about 12 cm. There is a short barbel at the snout, it swims swiftly, the body is a long spindle, slightly compressed, and the caudal fin is forked. As a juvenile the body color is a very pale mixed tone; as it nears adulthood it becomes greyish, and all fins turn red (though not vividly), shimmering under light — which is why it has always been popular.

The body is elongated and compressed, with a fairly flat belly profile. The mouth is terminal with a short barbel at the snout. The dorsal fin is high and triangular, set toward the middle-rear of the body, giving an overall shark-like silhouette. The body color is uniformly black, with males darker. All fins are deep black except the caudal fin, which is bright orange-red; the pectorals are pale or faintly orange-yellow.

3 Habitat & Living Environment

The suitable water temperature is 24–26°C. Although not demanding about water quality, note that Rainbow Sharks prefer mature (‘old’) water and should not be changed too often. As a relatively large bottom-dwelling tropical fish, they need a somewhat spacious tank, ideally planted with broadleaf aquatic plants.

They are egg-laying fish that use flower pots for spawning; sex is told by body shape and color — males are slimmer with golden-red tails, females slightly larger with orange-red tails. For breeding, keep the pair separate for about two weeks beforehand and feed plenty of live food; line the breeding tank bottom with black-and-white pebbles, plant broadleaf plants, and set an upturned flower pot. Use slightly acidic water at 25–26°C with a 1:1 male-to-female ratio. After two weeks the pair are united and usually spawn at dawn. This fish strictly practices ‘monogamy’ and will not tolerate a third male — two males will fight and one will be hurt, so pair them carefully. Rainbow Sharks like semi-dim surroundings, are rather timid, and enjoy hiding among plants.

4 Feeding Guidelines

The Rainbow Shark is easy to keep in captivity, but breeding it is fairly difficult. Because it is nicknamed the ‘cleaner’, it is omnivorous.

Although omnivorous, it loves live foods such as mosquito larvae and tubifex worms, and generally prefers live food — so you can feed more bloodworms in captivity. It swims actively and is aggressive as an adult, often attacking other fish and especially biting flowing fin rays, so it should not be mixed with long-finned fish such as angelfish; keep it in a group of similar-sized, robust tankmates.