Application of fish protein hydrolysates in common carp (Cyprinus carpio) diets for fish meal sparing: Evidence from growth, intestinal health and microflora composition

Fish protein hydrolysates (FPH) were applied in a 8-week feeding experiment with juvenile common carp (Cyprinus carpio) (initial body weight 8.75±0.05 g), to preliminarily investigate their effects on growth performance and feed utilization and potential influence on intestinal antioxidant status, expressions of protein synthesis gene and microflora. Common carp were fed with 0%, 0.5%, 1%, 1.5%, and 2% FPH (named as FPH-0, FPH-0.5, FPH-1, FPH-1.5, and FPH-2) respectively, substituting 0%, 13.33%, 28.33%, 41.66%, and 55.00% of dietary fish meal. Each diet was randomly fed to triplicate groups of 25 fish per aquarium. Feeding experimental results revealed that final body weight, weight gain rate and protein efficiency ratio in the FPH-0.5 treatment were significant higher than those in other treatments. The FPH-0.5 treatment had highest crude protein level when compared to the FPH-1.5 and FPH-2 treatments (P<0.05). Protease activity in FPH-0.5 treatment were markedly higher than those of the FPH-1.5 and FPH-2 treatments. Obvious increments in activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and glutathione (GSH) and decline in malondialdehyde (MDA) contents of the intestine were found in the FPH-0.5 treatment. Significant up-regulation in the intestinal expression levels of PI3K, Akt, TOR, S6K and 4EBP1 of common carp were found in the FPH-0.5 treatment. Proteobacteria abundance was obviously restrained in the FPH-0.5 treatment compared to other treatments, and the Cetobaterium abundance could been markedly elevated in the FPH-0.5 treatment, especially compared with other FPH-containing feeds. Overall, 0.5% FPH supplementation exhibited a sparing effect on fish meal in common carp feed on the premise of promoting the growth and strengthening the intestinal health.