Seasonal changes in growth and standard metabolic rate of juvenile perch, Perca fluviatilis L.

The maximum growth rate of juvenile perch, PercaJuviatilis L., at different constant temperatures and in naturally changing day‐lengths was studied in the laboratory. Standard metabolic rate was studied in starvation experiments at constant temperatures under short‐ and long‐day conditions. Growth occurred in temperatures above 8 to 10°C. In winter, from mid‐October until mid‐April, maximal growth was considerably reduced and was relatively slow but constant. The standard metabolic rate was reduced c . 50% under short‐day conditions. The seasonal change in metabolic rates, presumably controlled by an endogenous rhythm, was considered to be an adaptation to low food availability during the short winter days.