Red-tailed black shark

What it is

This species belongs to the carp family and resembles a small shark in shape and swimming style. Adults feature a deep black body that becomes deeper in the middle as they age, particularly females. The most striking feature is the bright red or orange caudal fin, which can fade if the fish is stressed. They possess an inferior mouth facing downward, two pairs of barbels, and large triangular dorsal and anal fins. Juveniles are thin and streamlined, while adults develop a more robust profile. The fish grows to about 16 centimetres, though some individuals reach 20 centimetres.

Where it lives

The red-tailed black shark is native only to Thailand. Historical records place it in the Mae Khlong, Chao Phraya, and Bangpakong river basins. It inhabits lowland streams, creeks, and rivers characterized by strong currents, dense vegetation, and rocky or sandy substrates. Once thought extinct in the wild between 1996 and 2011, single specimens have been rediscovered in recent years. However, populations remain highly fragmented and localized, with significant habitat degradation from dams and agricultural runoff affecting its survival.

How it lives

These fish are active bottom dwellers that patrol water columns near rocks and plants. They exhibit a shark-like oscillatory movement and are known jumpers, often escaping uncovered tanks. Their temperament varies from territorial to aggressive, especially toward their own kind. They establish territories and may harass slower or smaller tankmates. While generally omnivorous scavengers eating insects, algae, and detritus, they will consume dead animals if available. They are nocturnal and tend to be more timid as juveniles, requiring hiding spots to feel secure.

Breeding and life cycle

Natural spawning triggers and mate selection remain poorly understood among enthusiasts. In captivity, reproduction is achieved through hormone injections, a process introduced around 1987. This method causes significant stress, leading to mortality rates as high as eighty percent for both adults and fry. Vaccination against diseases like Streptococcus iniae has shown promise in reducing these losses. Breeding in home aquariums is nearly impossible due to the species' intolerance of conspecifics and aggression during reproductive phases.

Fish and people

The red-tailed black shark is a staple in the ornamental fish industry, with all current trade specimens being captive-bred. Thailand exported millions annually in the late twentieth century, and the fish remains popular globally. Hobbyists value its striking colouration and active behaviour. Care requires medium to large tanks with strong filtration, hiding places, and secure lids to prevent jumping. Compatible tankmates include fast-moving minnows and larger aggressive species, while slow fish and invertebrates are often bullied or eaten.

Status and threats

Listed as Critically Endangered, the wild population has suffered drastic declines. Causes include habitat destruction from dam construction, swamp drainage, and pollution from agriculture and domestic sources. While overharvesting for the aquarium trade was historically blamed, debate continues regarding its exact impact. Captive breeding programmes offer a buffer against extinction, though genetically suitable stock for reintroduction remains uncertain. Conservation efforts focus on ex-situ breeding and further research into population trends and ecological threats.

Questions people ask about Red-tailed black shark

Good reading and sources

• Red-tailed black shark on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data