Rainbow Shark (Epalzeorhynchos frenatum)

Epalzeorhynchos frenatum is native to the Mekong, Chao Phraya, and other major river systems of Thailand, Myanmar, and Laos, where it inhabits large river channels, floodplains, and clear streams with sandy substrates and moderate current. In the wild, the Rainbow Shark grazes on algae, detritus, and micro-organisms from the substrate and rocks.

The body is dark grey to jet black with brilliant red-orange coloration on all fins — the contrast between the dark body and vivid fins creates the dramatic appearance. Males develop small black dots on the tail fin with age and a slimmer body profile; females are generally larger and more robust. An albino variant (white body with red fins) is also available in the trade.

Despite the 'shark' common name, E. frenatum is entirely unrelated to true sharks — the name refers to the shark-like body shape and prominent dorsal fin. It is a cyprinid fish related to rasboras and danios.

Rainbow Sharks are territorial, particularly toward conspecifics and similarly-shaped bottom-dwelling fish (Red-tail Black Sharks, other Epalzeorhynchos species). Multiple Rainbow Sharks in the same tank will fight aggressively. Toward dissimilar mid-water fish, they are generally peaceful — occasionally chasing fish that enter their bottom territory but rarely causing injury.

Rainbow Sharks prefer soft to moderately hard, slightly acidic to neutral water: pH 6.5–7.5, hardness 5–15 dGH, and temperatures 22–28°C. They adapt to a range of conditions and are moderately hardy aquarium fish.

A minimum 200-liter aquarium is recommended — they are territorial and need adequate space to establish territory without constant stress. Provide hiding spots (caves, driftwood, rocks) in multiple areas to establish a home territory. Dense plantings, rocks, and aquarium structure create visual barriers.

Feed a varied omnivorous diet: algae wafers, sinking pellets, blanched vegetables, flake, daphnia, brine shrimp, and bloodworms. Include plant-based foods — they are significantly herbivorous in the wild.

Keep only one Rainbow Shark per tank unless the aquarium is very large (400+ liters). Never house with Red-tail Black Sharks, other Rainbow Sharks, or similarly-shaped bottom-dwellers. Compatible mid-water and upper-level tankmates include large tetras, barbs, danios, rainbowfish, and other robust community species that don't spend time in the bottom territory.

Weekly water changes of 25–30% maintain water quality. They are more active and bolder in larger tanks with more structure.