Red-Tailed Black Shark

Epalzeorhynchos bicolor

Also known as: Red-tail shark, Red-tailed shark, Redtail black shark

Water Parameters

• Temperature: 22–27°C
• pH: 6.5–7.8
• Hardness (GH): 89–268 ppm (5–15 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

One of the most striking and recognisable aquarium fish, and a hobby icon since the 1930s: a matte jet-black body tipped with a single brilliant scarlet tail, unmistakable and sold in nearly every shop. Like its cousin the rainbow shark it is not a true shark but a bottom-dwelling member of the carp family that claims and patrols a territory, and like the rainbow shark its beauty comes with a temper. Juveniles can be peaceful, but mature fish are assertively territorial, especially toward their own kind and other floor-dwellers, which is the source of most stocking trouble. Endangered in the wild, where its native Thai waters have been largely drained and developed, it survives almost entirely through farmed stock. One per tank, plenty of space, caves, and fast upper-water companions are the recipe for a hardy, long-lived, and genuinely spectacular centrepiece.

Tankmates

As with the rainbow shark, the rule is one per tank: red-tailed black sharks are territorial toward their own kind and toward the closely-related rainbow shark, and two in the same tank means relentless chasing and a dead loser. They are also territorial toward other bottom-dwellers, so corydoras, plecos, loaches, and similar are harassed in their floor space. The right tankmates are fast, mid-to-upper-water fish that stay out of the shark's zone: danios, larger barbs, rainbowfish, congo tetras, and denison barbs. Provide caves and broken sightlines so the shark has a territory and the others have escape routes. Will eat dwarf shrimp, and aggression escalates markedly as the fish matures.

Compatible with

• Zebra Danio
• Tiger Barb
• Gold Barb
• Boeseman's Rainbowfish
• Congo Tetra
• Denison Barb

Avoid keeping with

• Betta
• Rainbow Shark
• Bronze Corydoras
• Bristlenose Pleco
• Kuhli Loach
• Cherry Shrimp

Common Problems

• territorial aggression toward bottom-dwellers and its own kind
• fighting with rainbow sharks or other red-tails if housed together
• increasing assertiveness with age
• ich

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-20