Redox status of juvenile Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), fed diets supplemented with poultry liver protein hydrolysate as feed aditive

Plant ingredients, when used as substitutes for animal protein ingredients, can negatively influence fish growth. Thus, feed additives have been used to enhance feed consumption, nutrient utilization efficiency and stress tolerance under intensive management conditions. One such potential feed additive in aquafeeds is poultry liver protein hydrolysate (PLPH), which is rich in essential amino acids and has in vitro antioxidant and antibacterial properties. In this study, we aimed to evaluate the effect of poultry liver protein hydrolysate as feed additive on the productive performance of Nile tilapia reared in a water recirculation system and investigate stress responses and redox status after an air exposure challenge. Nile tilapia juveniles were randomly distributed in 24 aquariums and fed plant-based diets supplemented with increasing levels of PLPH (0, 10, 20, and 40 g/kg) over a 45-day period. At the end of the experiment, we did not observe a significant effect of PLPH on productive performance variables or body indices (P > 0.05). Air exposure triggered stress responses in fish, as evidenced by an increase in blood glucose (P < 0.05). However, PLPH supplementation did not mitigate this effect (P > 0.05). Regarding redox status, a quadratic effect of PLPH supplementation was observed on malondialdehyde (P = 0.003) levels, as well as the activities of superoxide dismutase (P = 0.015), catalase (P = 0.015), and glutathione S-transferase (P = 0.001). Optimum PLPH supplementation levels were estimated at 25.14, 25.91, 22.57, and 18.83 g/kg, respectively, for these redox parameters. Increasing PLPH levels decreased carbonylated protein contents (P = 0.001) but increased hydrogen peroxide levels in the gills (P = 0.006). Although PLPH supplementation improved antioxidant enzyme activity, and attenuated protein damage, it concurrently increased reactive oxygen species production and lipid peroxidation. Further studies are necessary to elucidate the underlying mechanisms of action by which protein hydrolysates influence the redox status of fish reared under intensive management.