Red-tail black shark

Quick facts

Adult size

12 cm

Lifespan

can live up to 10 years

Tank zone

bottom

Temperament

aggressive

Difficulty

intermediate

Water parameters

Temperature

22–27°C

pH

6.5 to 7.5

Hardness

5 to 15 dGH

Tank requirements

Minimum volume

200 L

Minimum length

100 cm

Flow

moderate

Lighting

any

Substrate

sand

Driftwood

preferred

Hiding spots

needed

Open swimming room

needed

Lid

required - jumper

Feeding

Diet: omnivore, feeds primarily at the bottom.

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.

Vegetable matter required (algae wafers, blanched zucchini, spinach).

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.

Habitat

Native to Thailand, specifically the Chao Phraya River basin and tributaries. Wild populations are critically endangered due to dam construction and habitat degradation. The IUCN lists the species as Critically Endangered. All aquarium specimens are commercially bred; the wild population is too small and too protected for collection. The jet-black body with a vivid red-orange caudal fin is instantly recognizable and one of the most distinctive color patterns in the freshwater hobby. The common name refers to the tail color, distinguishing it from the rainbow shark (which has red-orange on all fins). Adults reach 12–15 cm. Males may be slightly slimmer with a more sharply defined black body; females may be slightly rounder, but sexing is unreliable by external appearance. The species has been commercially bred since the 1970s and is a staple of the aquarium trade.

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 essentially 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

Bioload coefficient: 3.5 (similar to rainbow shark; moderate waste).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

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