Red-tail black shark

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: plant safe.

Feeding

Omnivore that grazes on algae and biofilm but needs supplemental feeding. Sinking pellets, algae wafers, frozen bloodworm, frozen brine shrimp, blanched zucchini, blanched peas. Feeds on the bottom. Claims food that drops into its territory and defends it from other bottom-feeders. Feed once or twice daily.

Compatibility

• Territorial bottom-dweller, same behavioral profile as the rainbow shark but generally considered slightly more aggressive. One per tank, no exceptions. Two red-tail sharks will fight until one is dead or so stressed it stops eating.
• Don't keep with rainbow sharks, Chinese algae eaters, or any other bottom-dwelling fish with a similar body shape. These trigger the strongest territorial response.
• Tankmates should be robust mid-water or surface-dwelling species: barbs, larger tetras, rainbowfish, danios. The shark claims the bottom and occasionally chases interlopers but mostly leaves fish in other zones alone.
• Aggression escalates with age. A 5 cm juvenile in a community tank is mild-mannered. A 12 cm adult in the same tank is the undisputed ruler of the bottom half.

Origin and habitat

Endemic to Thailand. Originally described by H.M. Smith in 1931 as Labeo bicolor from specimens in a tributary of the Chao Phraya River. Historically found in Bueng Boraphet (Thailand's largest lake), the Chao Phraya River south to Bangkok, and the Mae Klong and Bang Pakong basins. The species was declared extinct in the wild in 1996 due to habitat destruction from agricultural pollution, dam construction, and possibly overcollection for the trade. In 2011 a small population was rediscovered in the Chao Phraya basin, and in 2014 a single specimen was collected from the Mae Klong system. Listed as Critically Endangered by IUCN. All aquarium specimens are commercially bred, probably using hormones; no wild collection occurs. Jet-black body with a vivid red or orange caudal fin and a white-tipped dorsal fin; this distinctive color pattern makes it one of the most recognizable freshwater fish. Distinguished from the rainbow shark (E. frenatum) because the red-tail has red only on the caudal fin, while the rainbow shark has red on all fins. Grows to about 12–15 cm, though some sources report up to 16 cm. Territorial and aggressive, particularly toward similar-looking species; best kept as a single specimen.

Breeding

Not bred in home aquariums under normal conditions. All commercial breeding uses hormone injection. Without hormones, the species does not spawn in tanks. The combination of territorial aggression (preventing male-female pairing) and unknown natural spawning triggers makes home breeding impossible. Sexing is difficult and unreliable. Every red-tail shark in stores is farm-bred from Southeast Asian operations.

Common problems

Territorial aggression is the defining challenge (covered above). The fish is otherwise quite hardy. Ich in new purchases is standard. White spot disease (not ich; raised white lumps) occurs occasionally. The Critically Endangered conservation status concerns some hobbyists, but the species' survival in the wild is a habitat issue, not a trade issue; buying captive-bred red-tail sharks has zero impact on wild populations. Color loss (the red tail fading to orange or pink) indicates dietary deficiency or stress. Color-enhancing food with astaxanthin helps. The most common problem is behavioral: the keeper buys a cute 5 cm juvenile and discovers within months that they own a fish with the attitude of a much larger cichlid.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size