Hypophthalmichthys nobilis (Richardson, 1845)

Hypophthalmichthys nobilis View in CoL View Figure

Common name. Bighead carp.

Diagnosis. Distinguished from H. molitrix by: ● scaled keel from pelvic to anal / ● pectoral long reaching beyond pelvic origin / ● 240–300 long gill rakers / ● head length 27–35 % SL / ● dark-grey overall colouration, flank with dark, large, very irregularly shaped blotches. Size up to 1460 mm SL and 40 kg.

Distribution. Used in aquaculture in Europe, Asia, and North America. No reliable data on natural spawning in West Asia, spawning reported from Europe (Terek). This species is rarely used in aquaculture and may have already vanished from West Asia. Established reproductive populations in North America and Karakum Canal in Turkmenistan, Central Asia. No established population in Aral Sea basin. Native to Central and South China.

Habitat. Stocked in large rivers and almost all still waters such as lakes and ponds. Often escape from fish farms. In aquaculture, adults tolerate brackish water (up to 7 ‰) when stocked in estuaries and coastal lakes. In native range, in rivers with marked water level fluctuations, overwintering in middle and lower reaches. Foraging in shallow ( 0.5–1.5 m deep) and warm (above 24°C) backwaters, lakes, and flooded areas with slow currents. Spawns in deep, turbid, and warm water above 18°C (usually 22–30°C), with strong currents ( 1.1–1.9 m /s) and high oxygen concentrations.

Biology. Lives up to 20 years. Spawns first time at 5–6 years, 550–700 mm SL, and 5–10 kg (Russian Pacific basin), or even at 2–4 years (males) and 3–5 years (females) in Turkmenistan. Migrates long distances upstream at onset of rapid flooding and water level rise (April–July, depending on location). Spawning migration begins in mid–May at temperatures of 18–19°C and lasts until end of June (Terek). Spawns during floods. Stops spawning when conditions change and resumes when water level rises. Spawns in upper water layer or even on surface in June (Terek). Females lay up to 1.1 million eggs in 1–3 portions, depending on flood duration. Eggs are yellowish, transparent, and hatch after about 2 days at around 25°C while drifting downstream in a deep open water layer. If river is blocked or available river reaches are too short, eggs cannot drift long enough and fail to develop. After spawning, adults leave river and migrate to feeding areas. Larvae drift downstream and settle in floodplain lakes, shallow banks, and backwaters with little or no current. In autumn/winter, when temperatures drop to 10°C, juveniles and adults form separate large schools and move downstream to deeper areas in main river to overwinter. Feeds mainly on zooplankton and also on algae.

Conservation status. Non-native; stocked for commercial fisheries. There are reliable data on natural spawning in rivers of southern Russia (Terek), but whether eggs and larvae could complete development is unknown. Native wild stocks in Russia and China are declining.

Further reading. Holčík 1976 (introduction, Danube); Movchan & Smirnov 1983 (morphology, biology); Kottelat & Freyhof 2007 (summary of distribution and biology).