Seasonal variation of the biochemical composition of two Teleosts (Perca fluviatilis, L, Rutilus rutilus, L) and plankton in the Pareloup reservoir (Aveyron)

Studies in four years on body composition of perch (Perca fluviatilis) and roach (Rutilus rutilus) from Pareloup reservoir showed, some years, and especially in perch, a decrease in somatic lipids associated with either a slowing down or an interruption in protein accretion in summer. In late autumn, a compensatory growth was observed in fish which could have suffer from unfavorable dietary conditions in summer. The seasonal determination of phytoplankton and zooplankton biochemical composition indicated a maximal nutritional value in summer. Conversely, a decreasing of available quantity was observed in autumn what implies an extension of dietary spectrum in the two species. In summer, the interannual variability of population structure and available plankton biomass should explain the use of energy reserves in fishes during that season.