Overview
AT A GLANCE
- Common Name: Red-tailed Black Shark
- Scientific Name: Epalzeorhynchos bicolor
- Category: Fish
- Subcategory: Cyprinids
- Size: Total length: 12-15 cm (4.7-6.0 in)
- Weight: 30-50 g (1.1-1.8 oz)
- Lifespan: 5-8 years in the wild; up to 10-12 years in human care
- Diet: Omnivore / Algivore; periphyton, biofilms, filamentous algae, benthic crustaceans, insect larvae, rotifers, and plant detritus
- Habitat: Slow-moving lowland freshwater rivers, flooded agricultural floodplains, swamp margins, and silty riverbeds with dense submerged wood and rocks
- Range: Endemic to central Thailand, historically in the Chao Phraya, Mae Klong, and Bangpakong river basins; restricted to small remnant populations in the Mae Klong drainage
- Conservation Status: Endangered (IUCN Red List)
The Red-tailed Black Shark (Epalzeorhynchos bicolor), commonly known as the redtail sharkminnow or firetail shark, is a striking, iconic freshwater teleost endemic to the river systems of central Thailand. Despite its predatory common moniker, this species is not a shark; it is an agile, bottom-dwelling cyprinid belonging to the carp and minnow family Cyprinidae. Celebrated for its dramatic coloration—a velvety, pitch-black body contrasted against a dazzling, fiery blood-red caudal fin—it has achieved legendary status in global freshwater biology.
Ecologically, Epalzeorhynchos bicolor is an active grazer of biofilms and periphyton in seasonal river floodplains. By scraping algae, micro-crustaceans, and organic detritus from submerged logs and smooth river stones using specialized horny tubercles on its lips, it cleans benthic substrates and keeps algal overgrowth in check. Historically, it was an abundant migratory component of the Chao Phraya basin, undertaking upstream seasonal breeding runs into flooded wetlands during monsoon surges.
Biology and Physical Characteristics
Epalzeorhynchos bicolor possesses an elongate, torpedo-like fusiform body adapted for swift, darting swimming through river currents. Its dorsal fin is tall and falcate, creating the superficial shark-like profile that inspired its popular name. Its ventral surface is flattened, allowing it to rest securely against river rocks. Around its inferior, down-turned mouth are two pairs of delicate sensory barbels that detect benthic invertebrates in silty riverbeds. The skin is a deep, velvety jet-black, contrasting with the vibrant crimson-scarlet of the tail.
Behavior and Ecology
Red-tailed black sharks are intensely territorial and solitary benthic fish, spending their days establishing defended feeding territories centered around hollow submerged wood or rock crevices. They display fierce intraspecific aggression, chasing away other sharkminnows or fish of similar shape with swift displays of flaring fins and circling maneuvers. In the wild, they are migratory breeders, moving out of main river channels into inundated grassy floodplains at the onset of monsoon rains to spawn among submerged terrestrial vegetation.
Conservation and Human Impact
Epalzeorhynchos bicolor is classified as Endangered on the IUCN Red List. In the late 20th century, extensive dam construction along the Chao Phraya, canalization of riverbanks, and swamp drainage for agriculture destroyed its migratory routes, causing it to be declared Extinct in the Wild in 1996. Fortunately, a small remnant wild population was rediscovered in the Mae Klong river basin in 2011. While endangered in its native waters, millions are commercially propagated in Thai aquaculture facilities via hormone-induced spawning for the international ornamental fish trade.
Interesting Factoid
Despite being called a shark, the Red-tailed Black Shark is actually a member of the carp and minnow family and was once declared completely extinct in the wild before being miraculously rediscovered in a single Thai river in 2011.