The utilization of diets containing high levels of fish protein hydrolysate by turbot ( Scophthalmus maximus) juveniles

Abstract

A feeding trial was carried out to compare growth and feed utilization of turbot juveniles (mean initial weight of 58.5 g) fed diets including standard fish meal (diet A) or LT fish meal (diet B) from Denmark as the only protein sources, or standard fish meal and 5, 15 or 25% of a fish protein hydrolysate (diets C, D and E, respectively) as the protein source. The diets were formulated to contain 56% protein and 14% lipid and were prepared as dry pellets. At the end of the trial final weight of turbot fed diet B (173 g) tended to be higher than that of fish fed the other diets (126–155 g) but this difference was not statistically significant. Feed conversion ratio ranged between 0.9 and 1.2 and was not significantly different among groups. Furthermore, N retention (% N intake) was not significantly different among groups. Energy retention (EI) was significantly higher in fish fed diet B than in those fed diet C. Regarding whole body composition, at the end of the trial there were no significant differences in proximate composition among groups. Energy content was, however, significantly higher in fish fed diet B than in those fed diet C. ADC of the diets were determined in a separate trial, using settling columns for feces collection. The ADC of dry matter and energy were not significantly different among groups. The ADC of protein of diet B (77.8%) was higher than in the other groups but it was only significantly higher than that of diet C (74.2). It is concluded that turbot juveniles performed better with a diet including LT fish meal than standard fish meal as the only protein source. Partial replacement of fish meal with fish protein hydrolysate did not improve growth or feed utilization.