GROWTH OF JUVENILE DIPLOID AND TRIPLOID SALMON (Salmo salar) FED A STANDARD DIET AND AN EXPERIMENTAL DIET CONTAINING HIGH PROPORTIONS OF HYDROLISED PROTEINS.

Recent studies have revealed significant differences in gut morphology between diploid and triploid fish raised on the same diets and under similar conditions (Peruzzi et al., 2014). Morphological differences in the digestive system induced by the treatment or ploidy status could have an influence on nutrient utilization and performance capacity in triploids compared to diploids. In this work, we compared the performance of diploid and triploid salmon (produced by pressure shock) fed with an experimental diet containing high proportions of fish protein hydrolysate over a 38 weeks feeding trial. Results were analysed in terms of fish survival and growth as well as muscle enzyme activities (protein turnover), and skeletal malformations.

Overall, survival was higher (p<0.05) in fish fed standard diet than in those fed experimental diet, being 92% and 88% respectively, and with no differences between ploidy groups. At the end of the experiment, fish growth (body weight and length) was highest in triploids fed a standard diet with no significant differences among the remaining experimental groups. Condition factor varied among groups throughout the experiment and was generally lower in triploid than in diploid fish with no effects of diet. Data on muscle enzyme activities showed variations among groups at some sampling points. Percentages of vertebral deformities were very low among diploids and highest in triploids fed a standard commercial diet. Within triploids, the incidence of deformities in fish fed the experimental diet was nearly half of that reported for those fed a standard diet.

Under our experimental conditions, partial dietary replacement of fishmeal by a protein hydrosilate (CSPC) did not improve growth in triploid Atlantic salmon between start feeding and the end of the smoltification period. Initial higher mortalities in diploid and triploid fish fed the experimental diet could be ascribed to water stability of small pellets (0.5-1.0mm) related to lower binding properties as shown during their manufacture. Fish growth (bulk weight) was lower in fish fed the experimental diet in the initial phase of the feed trial but the diet containing high proportion of protein hydrolysed protein sustained growth during the end of the experiment. Interestingly, there was a positive effect of the experimental diet on the incidence of skeletal deformities among triploid fish.