South Korea

The Chinese false gudgeon, Abbottina rivularis, is a small bottom-dwelling cyprinid native to China, the Korean peninsula and southern Japan. It has been widely introduced elsewhere, including the Mekong and Salween basins, Taiwan, Turkmenistan and Kyrgyzstan, and is considered invasive. It has started to appear in the aquarium trade and should never be released into natural waters outside its native range.

The giant Chinese bitterling, Acheilognathus macropterus, is a bitterling from China, the Korean peninsula, northern Vietnam and southeastern Russia. It has been introduced to Japan and is considered invasive there. Typical adults are 100 to 150 mm, and it appears in the trade only irregularly. Like all bitterlings it spawns in living unionid mussels, and its wide range suggests it may be a group of closely-related species.

Iksookimia hugowolfeldi is a cobitid loach endemic to Korea, known from the Yeongsan and Tamjin river systems in the province of Jeollanam-do. It is most similar to I. longicorpus, of which it was first considered a geographical variant, and has narrow dark bars below the lateral line with densely arranged small spots above. It apparently prefers small, shallow rivers and streams with moderate to fast currents, and needs clean, well-oxygenated water.

Iksookimia koreensis is a cobitid loach endemic to Korea, relatively common in river drainages of northern and western South Korea. It is most similar to I. pumila, formerly treated as a subspecies, but has 10 or more dark bars on each flank, saddle-like markings along the back and irregular spots over the upper body. It apparently prefers small, shallow rivers and streams with moderate to fast currents, and needs clean, well-oxygenated water.

Iksookimia pumila is a small cobitid loach endemic to Korea, known only from the Baek River drainage in the south-west of the country. A dam built in the middle reaches of the river in the late 1990s has undermined its presence at some localities. It is most similar to I. koreensis, of which it was formerly considered a subspecies, but has fewer than 10 bars on each flank and only a few larger, vertically orientated blotches on the upper body.

Iksookimia yongdokensis is a cobitid loach endemic to Korea, known from four river drainages in the eastern province of Gyeongsangbuk-do. Most similar to I. longicorpus and I. hugowolfeldi, it has 9 to 13 dark vertical bars on the flanks, a small dark spot at the base of the upper caudal-fin lobe and a much smaller lamina circularis in males. It is most often seen in sluggish, shallow habitats with sand or pebble substrates in the mid-to-upper sections of rivers.

Kichulchoia multifasciata is a cobitid loach known only from river basins of southwestern Korea. It is restricted to shallow, fast-flowing, highly-oxygenated headwaters with riffles and runs, and needs clean, well-oxygenated water in the aquarium. It is most easily told from K. brevifasciata, its only congener, by its body patterning, wrinkled lips and short barbels.

The roundtail paradise fish, Macropodus ocellatus, is a labyrinth fish with an enormous range in China, Korea and Japan, north to the Amur River. It lives in ditches, rice paddies, marshes and river backwaters, where winter can freeze the surface and drop the water to 3 °C. It is sometimes referred to as M. chinensis in older literature, a name now considered a synonym of M. opercularis. Males are territorial when breeding and build bubble nests.

The medaka, Oryzias latipes, is a ricefish from Japan, Korea, Taiwan, eastern China, Laos and Vietnam. Long used as a model organism in genomic and experimental biology, it was the first vertebrate animal to mate in space, in the mid-1990s. The ornamental 'golden' variant is more often seen than the natural form, and a transgenic 'glowing' form is illegal to buy, sell or own within the European Union.

Rhinogobius giurinus is a goby found through much of China, plus Taiwan, the Korean Peninsula, Japan and the Red and Pha river basins in Vietnam. It appears to exist in a number of forms that differ in colour pattern, morphology or both, and it is unclear whether all of them are conspecific. Newly-imported wild fish tend to be aggressive towards conspecifics, so unlike most Rhinogobius it is best kept in sexed pairs.

The northern snakehead, Channa argus, is a large snakehead native to eastern China, southeastern Russia and the Korean peninsula. Growing to 850 mm, it is largely unsuitable for the home aquarium given its size and natural behaviour. Introduced populations, first intended for aquaculture, are now established in Japan, the United States, central Asia and parts of eastern Europe.

The barbel steed, Hemibarbus labeo, is a cyprinid widespread in eastern Asia between the Yangtze and Amur river basins. A predominantly riverine fish of clear, well-oxygenated running water, it forms schools just above the substrate as an adult, and some populations make annual spawning migrations. Adults lack dark spots on the body and have a long snout and well-developed lips.

Hemibarbus longirostris is a cyprinid native to far eastern Asia, including northeastern China, southeastern Russia, the Korean peninsula and Japan. A predominantly riverine fish, it lives in clear, well-oxygenated running water over sand, gravel, rock or mud, and adults tend to form schools just above the substrate in slower-moving sections.

The spotted steed, Hemibarbus maculatus, is a cyprinid widespread in eastern Asia between the Yangtze and Amur basins, including Taiwan and Hainan. It has 7–11 large blackish spots on each flank and a deep body with a clearly convex dorsal profile. A riverine fish of clear, well-oxygenated running water, it breeds in May and June, depositing its eggs among aquatic vegetation. It has probably been introduced to Vietnam and Laos, or records from there represent another species.

Hemibarbus mylodon is a cyprinid endemic to the Korean peninsula, where it occurs throughout North Korea and South Korea. A predominantly riverine fish, it lives in clear, well-oxygenated running water over sand, gravel, rock or mud, and adults tend to form schools just above the substrate in faster-flowing sections.

The Korean bitterling, Tanakia signifer, is endemic to the Korean peninsula, where it occurs in southern North Korea and northern South Korea. It is considered endangered in South Korea, where it lives only in the Han river system and many populations have been extirpated. It inhabits cool, clean, shallow water over coarse sand or gravel, and like all bitterlings it spawns in living unionid mussels.