Effect of dietary poultry meal and oil on growth, digestive capacity, and gut microbiota of gilthead seabream (Sparus aurata) juveniles

Abstract This study aimed to evaluate the effect of replacing fish meal by poultry by-product meal (PBM) in actual commercial standard diets for gilthead seabream juveniles on growth performance, diet digestibility, digestive function, intestinal microbiota, and provide an economic analysis of using PBM in practical diets. Six isoproteic and isolipidic diets were formulated including increasing levels (from 0 to 37.5%) of PBM in replacement of fish meal, corresponding to a fish meal protein replacement in the diets up to 83%. Each diet was randomly assigned to triplicate groups of fish (IBW 63 g) and the growth trial lasted 70 days. No differences between groups were observed on growth performance, voluntary feed intake, feed efficiency, nitrogen utilization, and whole-body composition. Digestive enzymes activity and the ADC of protein, phosphorus, and energy were also not affected by dietary treatment. Regarding gut microbiota, fish fed diet PBM22.5 showed higher species richness and diversity of digesta microbiota, but no differences between groups were observed in mucosa OTUs, richness, and diversity indices. The cost of diet formulation decreased with the dietary replacement of FM by PBM, highlighting the potential of poultry by-products inclusion in commercial diets. Overall, this study indicates that dietary FM could be replaced at least up to 83% with PBM in diets for gilthead seabream juveniles without affecting growth performance and feed utilization while improving the economic efficiency of these diets.