Sexual size dimorphism of two common European percid fish: linkage with spatial distribution and diet

Many fish species exhibit female-biased size dimorphism that may lead to spatial segregation of sexes. We selected two common European percids (Percidae, European perch Perca fluviatilis and ruffe Gymnocephalus cernua ) differing in total body size, reproduction mode, habitat use and diurnal activity, to test whether they display size dimorphism and its effect on habitat use and diet. Females were significantly larger than equally old males (by 76% in perch, 23% in ruffe). No differences in habitat use by sexes were found along depth and longitudinal gradients of reservoir or between inshore and offshore habitats. Perch females had fuller guts, but both sexes were equally likely to consume same prey items ( Leptodora kindtii , Daphnia spp . , Chironomidae larvae, fish). Both sexes of ruffe had similar stomachs fullness, but females preferred L. kindtii and males Asellus aquaticus . In summary, perch and ruffe show strong female-biased size dimorphism, but sexes do not segregate spatially. Their unequal sex-specific dietary demands are satisfied by higher feeding rate of female perch and by preference for different prey items in ruffe. The magnitude of dimorphism was related to species body size and reproduction mode being larger in larger species and in total spawner (perch).