The Estimation of Daily Rates of Food Consumption for Fish

SUMMARY (1) Previous studies on rates of gastric evacuation and food consumption are briefly reviewed and criticized. The truly quantitative studies show that the evacuation rate is usually exponential and is related to water temperature by an exponential or power-law function. These relationships have been ignored in most of the previous methods used to estimate the daily food consumption for fish in the field. (2) Two new methods are proposed and both assume that the rate of gastric evacuation is exponential. The rate of food consumption is assumed to be constant within the interval between sampling in the first method, and to decrease with time in the second method which also requires an estimate of the satiation ration. Equations are developed for both methods. (3) In a series of experiments with brown trout and perch, the first method usually provided close estimates of the daily food consumption even when feeding was restricted to short periods at infrequent intervals of time. The first method was inadequate, and the second method more appropriate, for larger fish feeding close to the maximum or satiation level. (4) The new methods are compared with some of the equations of earlier workers and the latter are shown to have often made erroneous assumptions that produced underestimates of the daily food consumption.