The application of radiography to the study of fish nutrition

The measurement of individual food consumption rates of fish held in groups using radiography has enabled the development of a new approach to fish nutrition trials. In order to compare diets, groups of individually numbered fish are fed different experimental diets over extended periods of time (similar to standard nutrition trials) and food consumption rates are measured regularly over the course of the experiment. Analysis of covariance is then used to compare regression coefficients, obtained from mean consumption-growth relationships, from each diet. The advantages of the approach are several: (1) differences in appetite between fish fed different diets are monitored; (2) fewer fish are needed to establish consumption-growth curves over a large range of consumption rates; (3) measured food consumption rates, not ration levels, are used to calculate 'true' growth efficiencies; and (4) other factors, such as absorption efficiency, trypsin activity, the concentration of free amino acids in tissues and protein turnover can be measured for individual fish and related to differences in food consumption between fish in the same group. The approach has been used successfully with a variety of species to compare the growth response of groups fed two or more diets.