Every species

The redhook, Myloplus rubripinnis, is a relative of the silver dollars from much of northern South America, including the Amazon and Orinoco. Commonly sold as a silver dollar, it can be told apart by its black-trimmed, red anal fin and grows much larger, to around 25 cm. Given a large enough aquarium, correct feeding and good water quality it should not pose many problems. It is still widely referred to as Myleus rubripinnis.

The black-barred myleus, Myleus schomburgkii, is a close relative of the redhook from parts of Venezuela, Peru and Brazil. The black vertical bar on the flanks distinguishes it, and it is a smaller adult fish, though it is sometimes offered for sale as a redhook. Also called the black-ear pacu and disc pacu, it should be kept in groups of at least five, and a tight-fitting lid is a good idea as it moves extremely quickly when startled.

Mystacoleucus argenteus is a cyprinid from the Salween and middle Irrawaddy basins in Myanmar and western Thailand. It is occasionally marketed as 'Burmese rainbow barb' and differs from the similar M. obtusirostris in lacking black-edged scales on the body. Little has been published since Day's original description of 1888. Vigorous when feeding, it can upset slow-moving or timid tankmates.

Mystacoleucus atridorsalis is a pelagic cyprinid considered endemic to the lower Mekong basin in Laos, Thailand and Cambodia. It favours flowing lowland river channels and moves into flooded forest during the wet season. A triangular blotch at the tip of the dorsal fin helps separate it from congeners, and like all Mystacoleucus it has a forward-pointing predorsal spine that can become entangled in an aquarium net.

Mystacoleucus chilopterus is a pelagic cyprinid from the middle Mekong, Chao Phraya and Mae Klong basins in Laos and Thailand. It favours flowing lowland rivers and swiftly-flowing forest streams with rock and gravel. The anal fin has a concave margin and the dorsal and caudal fins black margins, and like all Mystacoleucus it has a forward-pointing predorsal spine that can become entangled in an aquarium net.

Mystacoleucus ectypus is a pelagic cyprinid from the middle Mekong basin in Laos and Thailand, and may be endemic to the Khorat Plateau. It inhabits flowing lowland rivers and swift tributary streams with rock and gravel. It has a triangular blotch at the tip of the dorsal fin but no black fin margins or crescent-shaped scale markings, and like all Mystacoleucus it has a forward-pointing predorsal spine that can snag in a net.

Mystacoleucus greenwayi is a riverine cyprinid from the middle Mekong basin in Thailand and Laos and the Chao Phraya watershed. It favours clear, well-oxygenated running water over sand or gravel, often in rock and boulder-filled headwater streams. A schooling fish, it should be kept in a group of six or more alongside similarly-sized cyprinids, loaches and other riverine fishes, and like all Mystacoleucus it has a forward-pointing predorsal spine that can snag in a net.

Mystacoleucus lepturus is a riverine cyprinid known only from the upper Mekong basin in southern China, Laos and Thailand. It favours clear, well-oxygenated running water over sand or gravel. The body is relatively slender, with a black margin on the dorsal fin and many crescent-marked scales. Records from Vietnam and Hainan Island refer to other species. Like all Mystacoleucus it has a forward-pointing predorsal spine that can snag in a net.

Mystacoleucus obtusirostris is a riverine cyprinid found from Myanmar and southwestern China to Vietnam, Borneo, Sumatra and Java. Referred to as M. marginatus for decades, it is the most widely distributed member of the genus, and populations vary somewhat in colour pattern. It is occasionally marketed as 'Burmese rainbow barb'. A group of six or more is the smallest to consider, and like all Mystacoleucus it has a forward-pointing predorsal spine that can snag in a net.

The two spot mystus, Mystus bimaculatus, is a small catfish found only on the island of Sumatra in Indonesia. It inhabits peat swamps, and its natural habitat is in danger of destruction by human activity. Very peaceful with even the smallest fish, it is more outgoing in a small group of its own kind. Commercial breeders have bred it only by hormone injection.

Day's mystus, Mystus bleekeri, is a bagrid catfish from India, Pakistan, Nepal, Bangladesh, Bhutan, Myanmar and Indonesia. It superficially resembles the more common M. vittatus but grows larger, to around 155 mm, and has a much longer adipose fin. Peaceful and gregarious, it suits communities of larger fish, though adults will probably eat small fish, and it is more outgoing in a small group.

The Asian upside down catfish, Mystus leucophasis, is a bagrid catfish from rivers in Myanmar that spends most of its time swimming inverted. Often sold at only a couple of inches, it is confused with the much smaller Synodontis nigriventris but is a uniform black without countershading. It grows to around 300 mm, will eat smaller fish, is usually intolerant of its own kind and is unsuitable for the general community tank.

Mystus mysticetus is a peaceful bagrid catfish from rivers of Laos, Thailand and Cambodia. It migrates into flooded forest in the wet season and is apparently often seen living and feeding in large shoals with its congener M. multiradiatus. The only Mystus with laterally positioned eyes, it makes a good bottom dweller for communities of larger peaceful fish, though it will probably eat small fish when adult.

Mystus rhegma is a peaceful bagrid catfish from Laos, Thailand and Cambodia, where it inhabits rivers and flooded areas including fields. An irregular import, little is known about its natural behaviour. Gregarious, it makes a good bottom dweller for communities of larger peaceful fish, though it will probably eat small fish when adult.

Mystus singaringan is a large bagrid catfish from Cambodia, Thailand, Vietnam, Laos, Malaysia and Indonesia. Not often seen in the hobby, it grows to around 300 mm and is used as a food fish in many of its native countries. It can be territorial and aggressive, eats smaller fish and is usually intolerant of its own kind, so it suits a tank of bigger fish such as larger barbs and large cichlids.

The Chinese sailfin sucker, Myxocyprinus asiaticus, is a catostomid endemic to the upper and middle Yangtze River system in China, including the Min. The only Asian member of its family, it is traded as juveniles under names such as 'Chinese banded shark', almost always without mention of an adult size of almost a metre or a lifespan of 25 years or more. Wild populations are threatened by dams, pollution, overfishing and introduced species.

The golden dwarf cichlid, Nannacara anomala, ranges from the Rio Aruka in Guyana to the lower Rio Marowijne in Suriname. It is often found in flooded grassland in low-lying coastal areas, but most fish in the trade are mass-produced on farms in the Far East or Eastern Europe. Hardy and easy to breed, it is regarded as an excellent beginner's cichlid, though a female guarding fry can be very aggressive.

The striped dwarf cichlid, Nannacara taenia, is known only from the area around Belém in Pará state, Brazil. A fairly shy fish of small, densely planted streams, it tends towards a drab brown and is rarely seen in shops, so it is more often obtained through specialist cichlid dealers or amateur enthusiasts. The female guards the eggs in a small cave while the male guards the wider territory.

The one-lined African characin, Nannaethiops unitaeniatus, is a small citharinid from Cameroon, Nigeria, Gabon and both Congo republics. A shy, peaceful fish of streams, small rivers, lakes and ponds, it should be kept in a shoal. Not often seen for sale, it is often confused with similar-looking members of the genus Neolebias, and mature males are smaller, slimmer and more brightly coloured than females.

The African darter characin, Nannocharax brevis, is a citharinid endemic to parts of the River Congo basin in the Democratic Republic of Congo. Nannocharax are notoriously tricky to identify, and more than two species may be sold under the names N. brevis and N. fasciatus. They look superficially very similar to the South American darter characins of the genus Characidium, and this species probably inhabits swiftly-flowing rivers and streams.