Gymnocephalus cernua (Linnaeus, 1758)

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 819

Gymnocephalus cernua

Common name. Ruffe.

Diagnosis. Distinguished from other species of Percidae in West Asia by: ● two dorsals confluent. Size up to 200 mm SL.

Distribution. In West Asia non-native to upper Kura and Rioni ( Georgia). In Europe, native to Trace in Türkiye and Caspian, Black, Baltic, and North Sea basins, north to about 69°N in Scandinavia. In Black sea basin south to Kuban.Also, in Aral basin, Arctic Ocean basin eastward to Kolyma. Introduced into France west of Rhine, northern Italy, northern Great Britain, Neretva ( Croatia, Bosnia-Herzegovina), and Great Lakes region, North America and likely elsewhere.

Habitat. Eutrophic lakes, lowland and foothill streams. Prefers still or slow-flowing waters with soft bottoms and no vegetation. Most common in estuaries of large rivers, brackish lakes with salinities up to 10–12 ‰ and reservoirs. Generally increases in abundance with increasing eutrophication.

Biology. Females live up to 10 years, males up to 7. First spawn at 1–3 years, male a one year earlier than female. Spawns March–May until July in northern Europe on various substrates at depths of about 3 m or less. Spawns at temperatures above 6°C in north and above 10°C in south. Usually, a single female spawns with several males. Eggs become sticky in contact with water and adhere to rocks or plants. Females may spawn intermittently, laying eggs in two or more portions, usually separated by about 30 days in summer. Eggs from first batch are larger than those from second. Larvae have no or only a short pelagic larval stage, early transition to benthic life, secretive and solitary, do not form schools. Survival of larvae is poor below 10°C and above 20°C. Crepuscular or nocturnal. Well-developed cephalic lateral-line system and tapetum

lucidum in the eyes make it an efficient predator at night and in turbid waters. Usually feeds on benthic chironomid larvae and amphipods, which can be detected in upper layers of substrate through sensory channels on head. Pelagic in coastal lakes and tidal estuaries, feeding on zooplankton and fish. When coexisting in deep lakes, Perca fluviatilis and G. cernua sometimes occur at different depths, with G. cernua being more abundant in deeper layers.

Conservation status. Non-native.

Further reading. Hölker & Thiel 1998 (biology); Craig 2000 (biology); Epitashvili et al. 2020 (records from Georgia).