Seasonal Changes in Feeding and Relative Condition Factors of Grayling in a Stretch of the Middle Reaches of the Yenisei River
In 2009-2013, we studied the seasonal dynamics of the feeding spectrum and diet of grayling in a stretch of the middle reaches of the Yenisei River (from the dam of Krasnoyarsk Hydro-Electric Plant to the Kan River mouth) and traced its connection with the state of food supply and fish growth. It was shown that the intensity of fish nutrition was relatively stable throughout the year, despite significant fluctuations in zoobenthos biomass. The contribution of groups that were dominant in the diet - amphipods and larvae of caddis flies - changed depending on the month. Amphipods dominated in the diet of fish in the period from June to October, caddis flies - in the winter and spring months. Among caddis flies, a certain small species Apatania crymophila was consumed. The change of the primary diet component during the summer period corresponds to a sharp increase in the coefficients of relative condition factors, with a peak in August and September. It is assumed that the change in the rate of fish biomass accumulation is associated not only with an increase in water temperature, but also with switching of grayling to consumption of nutritionally more valuable amphipods.