Hypophthalmichthys molitrix (Valenciennes, 1844)

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 428-429

Hypophthalmichthys molitrix

Common name. Silver carp.

Diagnosis. Distinguished from H. nobilis by: ● sharp scaleless keel from pectoral region to anal origin / ● pectoral short, not reaching beyond pelvic origin / ● 650–820 long, slender gill rakers / ● head length 24–29 % SL / ● plain silvery colouration, greenish-grey above, whitish below. Size up to 1000 mm SL and 50 kg.

Distribution. Introduced in most drainages in West Asia. Established reproductive populations in North America, in Karakum Canal in Turkmenistan, Central Asia, potentially also in Danube (Europe). No established population in Aral Sea basin. Native to most major Pacific drainages in East Asia from Amur to Xi Jiang. Used in aquaculture almost worldwide outside of tropics.

Habitat. Stocked in large rivers and almost all still waters such as lakes, reservoirs, and ponds. Often escapes from fish farms. Aquaculture tolerates brackish water (up to 7 ‰) when stocked in estuaries and coastal lakes. In its native range, inhabits rivers with marked fluctuations in water level, overwintering in middle and lower reaches. During feeding season in shallow (0.5–1.0 m deep) and warm (above 21°C) backwaters, lakes, and flooded areas with slow currents. Spawns in rivers or tributaries above shallow rapids with gravel or sand bottoms, strong current ( 0.5–1.7 m /s), turbid water, temperatures above 15°C (usually 18–26°C), and high oxygen concentrations.

Biology. First spawns at 5–7 years. Juveniles and adults form large schools during spawning and overwintering. Migrates long distances upstream at onset of rapid floods and water level rise (April–August depending on location; late April– early June in Terek), able to jump over obstacles up to 1 m.

Spawns during floods when water level rises 50–120 cm above normal, usually at 18–26°C. Stops spawning when conditions change (particularly sensitive to falling water levels, reduced turbidity and increased current velocity) and resumes spawning when water levels rise. Spawns in upper layer of water or even on surface. Females lay about 500,000 eggs in one or more portions, depending on duration of flood. Eggs float, are transparent, and hatch after about 2 days at about 25°C while drifting downstream. If river is blocked or if 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. In autumn–winter they migrate to deeper places in mainstream, where they remain without feeding. Larvae drift downstream and settle in floodplain lakes, shallow banks, and backwaters with little or no current. Feeds from about 15 mm SL on phytoplankton only. Very sensitive to low temperature (below 5°C) and oxygen depletion. There is reliable data on natural spawning in rivers of southern Russia (Terek) and lower Danube. Still, it is not known whether eggs and larvae could complete development. There is no evidence that this species has become established in West Asia or North Africa.

Conservation status. Non-native; stocked for commercial fisheries. Survives in West Asia and Europe only through stocking. Potentially reproductive in Danube. Native wild stocks in Russia and China are declining.

Further reading. Holčík 1976 (introduction, Danube); Movchan & Smirnov 1983 (morphology, biology); Howes 1981 (anatomy); Kottelat & Freyhof 2007 (summary of distribution and biology).

Hypophthalmichthys nobilis ; Shanghai Aquarium, ~ 350 mm SL.© Zhou Hang.