MODELING THE INCREASE IN VARIANCE OF FISH WEIGHT

A simple model is described that is very effective in accounting for the variance in fish weights in groups of fish grown under controlled environmental conditions. The model explains the increase in variation over time in terms of final weight and the time required to reach this weight and is independent of initial weight and feeding rate. Results from experiments with rainbow trout (Oncorhynchus mykiss) and Arctic char (Salvelinus alpinus) were used to confirm the model's fit and to demonstrate how temperature effects can be incorporated. We discuss the use of the model for prediction and for testing for genetic or environmental effects on variation and for quantifying such effects on variance over time.