Ctenopharyngodon idella (Cuvier and Valenciennes, 1844)

Ctenopharyngodon idella View in CoL View Figure

Common name. Grass carp.

Diagnosis. Distinguished from similar Mylopharyngodon piceus by: ● body olive to brassy green on back, silvery white to yellow on flank / ○ body cylindrical / ● pharyngeal teeth laterally compressed, serrated, with a groove along grinding surface ( Figure 43 View Figure 43 ), usually in two rows, 2,5–4,2. Size up to 1200 mm SL and 32 kg. Distribution. Rarely introduced for weed control or escaped from aquaculture facilities. No established populations in West Asia. Native to East Asia, in most major Pacific drainages from Amur to Xi Jiang. Used in aquaculture in Asia, Europe, and North America; released in most major drainages. Established non-native populations in North America and in Aral Sea basin (Central Asia).

Habitat. Stocked in large rivers and almost all still waters such as lakes, reservoirs, and ponds. Often escapes from fish farms. In its native range, inhabits rivers with pronounced water level fluctuations caused by floods. Spawning and overwintering in middle and lower reaches of large rivers. In lakes, reservoirs, and backwaters during feeding season, preferably in warm, clear water with high oxygen concen- trations.

Biology. In natural habitat, first spawns at 7–10 years and about 600–800 mm SL, females 1–2 years later than males. Spawns April–August. Migrates upstream and spawns during high water, in upper water layer, or on surface in sections with strong currents. Females lay one or more por- tions of eggs depending on length of flood. Average females lay about 1.5 million pelagic eggs, hatching while drifting downstream in 2–3 days; 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 flooded areas, lakes, or backwaters with dense vegetation. They return to river in autumn–winter and spend cold season in deep places in lower reaches. Larvae settle in flooded lakes and channels with little or no current after a downstream migration of about 1000 km. Larvae feed on phyto- and zooplankton and then, from about 25 to 50 mm SL, on aquatic macrophytes. Larger juveniles and adults feed mainly on macrophytes, including terrestrial macrophytes, during summer floods. Does not feed in winter. There are reliable data on natural spawning in rivers in southern Russia, but success of these reproductive events is not known.

Conservation status. Non-native; stocked for commercial fisheries. In West Asia very rarely stocked. Native stocks in eastern Russia and China are declining. Its introduction into Czech Republic was accompanied by introduction of tapeworm Bothriocephalus gowkongensis , which subsequently caused severe losses in Cyprinus carpio farmed stocks.

Further reading. Bíró 1999a (biology); Nico et al. 2001 (comparison with Mylopharyngodon ); Kottelat & Freyhof 2007 (summary of distribution and biology).