red-tailed black shark

The red-tailed black shark (Epalzeorhynchos bicolor; syn. Labeo bicolor), also known as the redtail shark, red tailed shark, and redtail sharkminnow, is a species of tropical freshwater fish in the carp family, Cyprinidae. It is named after its shark-like appearance and movement, as well as its distinctive red tail. Despite its name, it is more closely related to carp. It is endemic to streams and rivers in Thailand and is currently critically endangered. However, it is common in aquaria, where it is prized for its deep black body, and vivid red orange tail. These are moderately sized tropical aquarium fish who are active benthic swimmers. They are omnivorous but are willing to scavenge if the opportunity arises. They are known for their activity as well as their temperament towards other fish. The red-tailed black sharks seen in the aquarium trade today are all captive bred.

This species is endemic to Thailand, and has been recorded in the lower Mae Khlong, Chao Phraya, and Bangpakong river basins. It was described by Hugh McCormick Smith in 1931 as being "not uncommon in Borapet Swamp, Central Siam, and in the streams leading therefrom", and as being found in the Chao Phraya River as far south as Bangkok. A 1934 expedition reported catching a specimen in the Silom canal. Red-tailed black sharks live in lowland streams, rivers, and creeks. They prefer areas with high flow, dense vegetation, large rocks and rocky or even sandy sediment. However, from 1996 until 2011 it was believed to be extinct in the wild. In 2011 it was only known at a single location in the Chao Phraya basin, however it was believed to be strictly localized and is thought to be extirpated across the rest of its range. However, a single specimen was found in 2013 in a rocky dam around the mainstream of the Mae Khlong River in the Muang District of West Thailand.

Red-tailed black sharks are omnivorous scavengers who are rarely picky eaters. In the wild they eat insects, small crustaceans, worms, detritus, and plant matter. They will also eat algae off rocks, plants, and décor similar to many popular sucker fish in aquariums. They will scavenge recently deceased fish and animals if given the chance. They generally patrol the bottom of the water column around rocks and plants searching for food.

Red-tailed black sharks are fast active swimmers that patrol the bottom of the water column. Their movement is reminiscent of sharks as they glide through the water with an oscillatory style of movement. They are known to be good jumpers and can jump out of most aquariums without a lid. Red-tailed black sharks are territorial and aggressive to other fish, and especially intolerant of other red-tailed black sharks. They will establish their own territory and will harass and chase other fish within its territory, though having a larger space with plenty of hiding places can dissipate their aggression. They may bully other fish that are smaller and slower to compete for food or space. However, their behavior and treatment towards other fish does depend on the temperament of the individual. There are cases of red-tailed black sharks living peacefully with tankmates so long as their position and territory goes unchallenged. Because of this, they are usually labeled by hobbyists as semi-aggressive since their temperament can range from territorial to hot tempered depending on the individual. They are solitary and will be aggressive and may even attack members of their own species who may compete for territory or food. Juveniles however tend to be more timid than adults, and require more hiding places to feel comfortable. Red tailed-black sharks are also nocturnal, being more active at night.

Red-tailed black sharks grow to be 6 inches (16 cm), but some specimens have reached 7–8 inches (18–20 cm). They have a black elongated body shape that is moderately compressed, and with the snout overhanging the mouth. As juveniles they are all thin and streamlined. However, as they age their bodies becomes deeper in the midsection, which is most prominent in females. Red-tailed black sharks have an inferior mouth that faces downwards, as well as two pairs of barbels around it. Some specimens may have small black spots just above the lateral line that can be difficult to spot in life.

Currently the Red Tailed Black Shark is listed as Critically Endangered on the IUCN Red List. The reason as to why the wild population has declined is not well known. Intense overharvesting by the aquarium trade has historically been blamed for being responsible for the species' decline. However, this claim is still being debated with little documented evidence available to support this claim. It could be argued that the aquarium trade saved the species from extinction, as breeding of red-tailed black sharks in countries such as Thailand and Sri Lanka has relieved pressure off of harvesting wild populations. Presently, current wild populations are threatened by pollution from agricultural and domestic sources, as well as from habitat modification and degradation. The construction of dams during the 1970s, the drainage of vast areas of swamp land, as well as additional infrastructure development such as road building likely caused great loss of habitat. Pollution runoff from farmlands and domestic sources may have caused changes in flow regimes and siltation to unsuitable levels. Despite the many threats, the scope and severity that these fish face is currently unknown.

The fins are all black except for the caudal fin, and occasionally the pectoral fins, which can be orange or red. Its caudal fin is forked and colored a bright red that extends to the last few scales of the caudal peduncle. The coloration of the tail can dim or fade when the individual is stressed, sick, or in poor water conditions. The pointed lobes of the caudal fin are longer and larger than its head. The dorsal fin is large and triangle shaped. It is the largest fin on the fish with the longest ray being as long as the fish is deep. The dorsal fin starts midbody but goes as far back as the peduncle, and occasionally having a white tip at the top. The anal fin is also large and triangular but smaller than the dorsal fin. The rays of the anal fin almost reaches the base of the caudal fin. The pelvic fins are triangular, are located ventrally and at the midbody, and are smaller than the anal and dorsal fins. The pectoral fins are shorter and placed lower on the body but not ventrally. The pectoral fins are often more transparent than the other fins and can be either black, clear, or orange in color. It is difficult to discern sex of individual until around 15 months old. Females tend to be larger and wider than males. While males have brighter colors, slimmer bodies, and pointer dorsal fins.