Growth of Atlantic salmon (Salmo salar L.) in a variable diel temperature regime

In five experiments, Atlantic salmon (Salmo salar L.) parr were found to grow better under conditions of rhythmically alternating water temperature (P<0.031), than control groups reared under stable temperature conditions. The daily temperature sums for the experimental and the control groups were carefully equalized and monitored in all five experiments. The experimental group was reared in a rhythmically alternating temperature regime, of 10.0 h of high temperature (16.0°C) and 10.0 h of low temperature (10.0°C), the temperature adjustments being made during the 2 h between the periods of fixed temperature. The control group were reared in a relatively stable temperature regime (13.00–13.98°C). The growth rate of the fish reared under the varying temperature conditions was higher (mean for all five experiments 1.96% day⁻¹) than that for the salmon reared under stable conditions (1.85% day⁻¹).