Rainbow Shark ~ Epalzeorhynchos frenatum

The Rainbow Shark is an energetic and visually striking freshwater species recognized by its sleek black body paired with vibrant red or orange fins. Native to river basins and floodplain wetlands in Thailand, Laos, and Cambodia, this fish is often mistaken for a community species because of its moderate size, but it is actually territorial and assertive, especially toward similar-shaped bottom dwellers. Its streamlined shape, constant activity, and intense coloration make it a bold, dynamic presence in large, well-structured aquariums.

• Size: 5-6 inches

• Lifespan: 5-8 years

• Temperament: Semi-aggressive, territorial

• Group/Solitary: Kept singly; multiple require very large tanks with distinct territories

• Food: Omnivorous, sinking pellets, spirulina, algae wafers, live/frozen foods like bloodworms and brine shrimp

• Water Requirements: 72-79°F, pH 6.5-7.5, moderate hardness

Rainbow Sharks thrive in spacious aquariums with plenty of hiding spots, driftwood, rockwork, and dense planting that allow them to claim a territory without constant conflict. A minimum tank size of 55 gallons is recommended, as these fish are active swimmers that patrol the lower levels of the tank. Appropriate tank mates include fast-moving midwater species such as robust barbs, danios, and rainbowfish. Slower or bottom-oriented fish should be avoided, as they may be harassed or outcompeted. Diet should consist of a balanced mix of algae-rich foods and protein sources to maintain color vibrancy and overall health. Clean, well-oxygenated water with stable parameters is essential.

In the wild, Rainbow Sharks inhabit shallow rivers, streams, and seasonally flooded plains with sandy or muddy substrates. These environments contain scattered vegetation, submerged wood, and organic debris that support algae, biofilm, and small invertebrates—their natural diet. They are most active during dawn and dusk when they forage along the bottom and defend feeding areas from rivals.

Fun Fact: The vivid red fins of the Rainbow Shark become brightest when the fish is healthy, well-fed, and in a stable territory, making its coloration a strong indicator of aquarium conditions and social comfort.