Redtail Black Shark (Epalzeorhynchos bicolor)

The Redtail Black Shark (Epalzeorhynchos bicolor) is one of the most iconic aquarium fish — its velvety black body and vivid scarlet-red caudal fin create a dramatic contrast that has made it a perennial favorite. Native to the floodplains and streams of central Thailand, it was once common in its native habitat but is now considered Critically Endangered in the wild due to habitat destruction and overcollection. Virtually all specimens in the hobby today are captive-bred.

Despite its 'shark' common name, this fish is a member of the carp family (Cyprinidae) and is not related to true sharks. The name refers to its distinctive upright dorsal fin. It is a bottom and mid-level fish that is highly territorial toward its own kind and similar-looking species — only one individual should be kept per aquarium.

The Redtail Black Shark can be aggressive toward other fish that are slow-moving or share its benthic territory, but generally ignores fast-moving mid-water fish. It grows to about 12–15 cm and requires a spacious aquarium with plenty of caves and hiding spots to establish territory.

As an omnivore, it accepts a wide range of foods including algae, biofilm, sinking pellets, blanched vegetables, and frozen meaty foods. Providing driftwood and flat rocks for grazing helps satisfy its natural foraging behavior.

Water Parameters: Redtail Black Sharks prefer pH 6.5–7.5, temperature 22–26°C, GH 5–15. Moderate hardness and neutral pH replicate their native conditions. Good filtration with moderate flow is beneficial. They are sensitive to poor water quality.

Tank Setup: Minimum 150 liters for a single specimen. Provide caves, overhangs, driftwood, and PVC pipe sections to establish territorial boundaries. Open mid-water swimming space with robust plants along borders. A dark substrate highlights their black coloration. Avoid keeping multiple individuals — severe aggression results.

Feeding: Omnivore with a preference for algae and biofilm. Supplement with sinking algae wafers, blanched zucchini, spinach, and occasional frozen bloodworm or brine shrimp. Feed once daily in the evening. Avoid overfeeding.

Tankmates: Best kept with fast-moving, robust upper to mid-water fish that don't compete for bottom territory: tetras, barbs, danios, and rasboras. Avoid other bottom-dwelling territorial species, or fish resembling the Redtail Shark. Remove immediately if aggression becomes problematic.

Health: Generally hardy. Common issues include ich and bacterial infections if water quality drops. Their bold behavior means injuries can occur in inappropriate setups — ensure adequate space and hiding spots. Perform regular water changes of 25–30% weekly.