Field observations and laboratory experiments on growth and lipid content of young-of-the-year perch

Differences in growth and allocation of energy of young-of-the-year (YOY) perch (Perca fluviatilis) were studied in relation to both quantity and quality of food. Feeding on fish and Mysidacea, the mean size of YOY perch after the first growing season in Lake Pfeiffer was 152 mm. In contrast, YOY perch grew to 107 mm in Lake Speldrop and 83 mm in Lake Reeser Meer while mainly feeding on zooplankton. In correlation with food uptake and growth, the lipid content of YOY perch was significantly highest in Lake Pfeiffer and lowest in Lake Reeser Meer, assuming that YOY perch from Lake Pfeiffer should be able to survive starvation periods during their first winter better then those from Lake Speldrop and Lake Reeser. While feeding on fish, mean highest growth rates were 1.31 mm center dot day(-1) in the laboratory. Growth in weight started when food uptake exceeded 66 J center dot g WW-1 center dot day(-1), while an increase of lipid content required food input of 175 J center dot g WW-1 center dot day(-1). Increased growth potential associated with the availability of energetically profitable food is assumed as an important factor that could have far-reaching consequences for the fish community.