Estimation of the daily ration of fingerling sea bass, Dicentrarchus labrax, using a radioisotope method

A previously developed method for the estimation of the daily ration of fingerling sea bass, based on the counting of radioactivity after feeding an 125IAg-labelled diet, was further studied in 1.25 g fingerlings of the same species. Fish were fed separate meals of three experimental diets differing only in protein source. Labelled diets were offered instead of regular diets in order to estimate feed intake. Radioactivity was measured individually on the whole body of 15 fish per group using a gamma-counter and feed intake was calculated using standard equations established for samples of labelled feeds. Maximal voluntary ingested ration and maximal daily ration were then calculated. The maximal daily ration was found to be 3.5% of body weight irrespective of protein source. This method is very rapid and permits estimations of the above parameters which corroborate other measurements and have a low standard deviation.