Effects of yeast hydrolysate supplementation in low-fish meal diets for pikeperch.

Plant proteins have been increasingly used as sustainable substitutes for fish meal (FM) in aquafeeds; however, their high inclusion level compromises fish performance. The objective of this study was to examine whether yeast hydrolysate (YH) supplementation can improve the utilisation of high soybean meal (SM) diet and ameliorate its potential deteriorating impacts in pikeperch (Sander lucioperca). A basal diet was formulated using 44% FM, and four additional diets were produced by replacing 30 or 60% of FM with SM with or without the addition of 2% YH (FM, SM30, SM60, SM30 + YH, and SM60 + YH diets). Each diet was fed to three groups of fish (35.3 ± 0.10 g, 150 fish per group) to visual satiety four times daily for 70 days. Fish growth was not impacted by FM replacement level or YH application. However, SM60 group exhibited markedly higher feed conversion ratio and lower survival rate than those fed the FM- and YH-supplemented diets (P < 0.05). The highest and the lowest protein efficiency ratio values were obtained for the SM30 + YH and SM60 groups, respectively. Whole-body lipid content decreased in SM60 and SM60 + YH groups, and muscle lipid decreased in all the replacement groups. Serum triglyceride and glucose concentrations tended to decrease as FM replacement level increased. The highest alanine aminotransferase, aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) activities were detected in the SM60 group, and YH addition significantly decreased the AST and LDH activities. Serum lysozyme activity decreased in SM30, SM60 and SM60 + YH groups. Serum myeloperoxidase and antiprotease activities decreased in SM60 group, and YH supplementation improved their activities. No effects of diets were observed on serum antioxidant parameters such as catalase activity and malondialdehyde concentration, and gut morphological indices. Number of goblet cells in midgut decreased by increasing the SM inclusion level and a slight improvement was observed by YH application. These findings suggest that YH supplementation has the potential to support the replacement of up to 60% FM with defatted SM in pikeperch feed without deteriorating growth, feed utilisation, and survival rate. Further, YH incorporation mitigated the damaging impacts of high SM diet on liver function and non-specific immune response.