Morphological and behavioral variation in juvenile roach Rutilus rutilus (Cyprinidae, Cypriniformes) from different biotopes of the Rybinskoe Water Reservoir

Behavioral mechanisms of trophic differentiation in benthivorous fish

“…The possibility of associated inheriting of the features in the migrants is confirmed by the fact that coefficient of variation of morphological features in these fish hardly changes after appearance in the open littoral (Stolbunov and Gerasimov, 2008). The diapason of variability of sizes of mouth apparatus in the juvenile roach obtained by directed individual hybridization of "small mouthed" parents coincides with that one in the same type juve nile roach from the wild and significantly differs from the relevant parameters of the large mouthed morph indicating inheriting of specific features of structure of mouth apparatus (Stolbunov, 2005).…”

“…In the studies at the Upper Volga basin, trophic differentiation was revealed in the populations of such mass species as bream and roach (Kasyanov et al, 1982;Kasyanov and Izyumov, 1995; Poddubnyi, 1999;Gerasimov, 2006;Gerasimov, 2007;Stolbunov and Gerasimov, 2008).…”

“…Proof of this may be that adult mol luscivirous and coastal roach have the same ratios in the sizes of mouth opening as juvenile fish (Fig. 11) (Stolbunov and Gerasimov, 2008). The sizes of mouth in the adult fish do not lack adaptive importance since mollusks of g. Dreissena may reach large size.…”

“…However, our recent morphological investigations of juvenile roach from various habitats (Stolbunov and Gerasimov, 2008) revealed that the differentiation of roach to two morphotypes may already be tracked as early as during the initial developmental stages. Above mentioned morphotypes are characterized by spatial segregation in two biotopes: open littoral, non protected of waves (sandy grounds devoid of macro phytes) and protected shallows (macrophyte over growths in the river mouths and in the islands lee areas).…”

“…This provides these fish with a higher rate of survival in the quite aggressive environment of open waters characterized by active hydrodynamics, lack of shelters, domination of chas ing predators, and large active pelagic zooplankters serving as food. Laboratory experiments proved that the juvenile roach caught in the open littoral possess better swimming ability and more efficient defensive behavior compared to the juvenile fish from protected shallows and mean size of food organisms in the food of juvenile roach is larger in the open biotopes than in the protected shallows (p < 0.001) (Stolbunov and Gerasimov, 2008).…”