Rainbow shark
Epalzeorhynchos frenatum
intermediate careOverview
The rainbow shark (Epalzeorhynchos frenatum) is a striking bottom-dweller: a dark grey-black body set against bright red fins, with a shark-like profile that gives it its name. It’s an active, characterful fish — and a territorial one. Rainbow sharks patrol the lower levels of the tank and grow more assertive with age, so success comes down to a big enough tank, the right tankmates, and usually keeping just one.
Tank & water
Adults reach 12–15 cm and claim territory along the bottom, so a single fish needs a minimum of 190 litres (50 gallons) with a long footprint.
- Territory and cover: lots of caves, wood and plants to break sightlines gives the shark a home base and reduces conflict.
- Water: pH 6.5–7.5, 24–27 °C with a reliable heater, and clean, well-filtered water from a good filter.
- Mature tank: cycle fully and let algae and biofilm develop before adding one.
- A lid: they can dash and jump when startled.
Feeding
An omnivore that grazes the bottom, the rainbow shark eats sinking pellets and wafers, quality flakes from the fish food range, and appreciates algae, blanched vegetables and occasional frozen foods like bloodworm and brine shrimp. It will rasp at algae but is not a dedicated algae-eater — don’t rely on it to clean the tank.
Tankmates
Best paired with peaceful mid- and upper-water fish that stay out of its floor territory: larger tetras, barbs, rainbowfishes, danios and gouramis. Avoid other bottom-dwellers that resemble it — other sharks, similar loaches — and anything small or timid it can bully. Keep it as the only rainbow shark in the tank.
For companions that share the space rather than the floor, see our best centerpiece fish for a community tank answer, and plan space with the best large aquarium guide.
Common mistakes to avoid
- Keeping more than one in a normal-sized tank
- Too small a tank with nowhere to hold territory
- Pairing with look-alike bottom-dwellers
- Expecting it to work as an algae-eater
Rainbow shark — frequently asked questions
Can I keep two rainbow sharks together?
Generally no. Rainbow sharks are territorial loners that fight other rainbow sharks and similar bottom-dwellers, often to the death in anything but a very large, heavily broken-up tank. In most home aquariums, keep just one.
Are rainbow sharks aggressive?
They are semi-aggressive and become more territorial with age, especially toward the bottom of the tank and toward look-alike species. In a big tank with mid- and upper-water tankmates and plenty of cover, a single rainbow shark is usually manageable.
Is a rainbow shark a real shark?
No — it's a member of the carp and minnow family, named for its shark-like shape and upright dorsal fin. It stays around 12–15 cm and has none of a true shark's biology.
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