Abstract
A 56-day feeding trial was conducted to investigate the effects of dietary proteolytic soybean meal (PSM) on growth performance, immune-related genes, and resistance against Vibrio alginolyticus in Litopenaeus vannamei. Six dietary levels of PSM (0, 35, 45, 55, and 65 g/kg) were added to a basal diet. The results showed that juveniles fed more than 45 g/kg PSM exhibited significantly (P < 0.05) promoted growth performance compared to the control. Furthermore, all PSM supplemented treatments showed significantly better performances in terms of feed conversion ratio (FCR), the protein efficiency ratio (PER), and the protein deposition ratio (PDR). Corresponding to the performances on growth and nutrient utilization, a significantly higher protease activity in hepatopancreas was also obtained in all PSM incorporations. Also, the activities of immune-related enzymes such as superoxide dismutase (SOD) and lysozyme in serum were significantly (P < 0.05) elevated in shrimp fed with PSM. Notably, shrimp fed with the 65 g/kg PSM supplemented diet showed significantly (P < 0.05) lower cumulative mortality compared to the control after challenging with Vibrio alginolyticus injection at 72 h. PSM supplementation significantly (P < 0.05) upregulated expression levels of immune deficiency (IMD) and Toll-like receptor 2 mRNA in shrimp gill tissues directly or indirectly reflected their activation effect in shrimp innate immune response. In conclusion, the current study proved that partial replacement of soybean meal with PSM could result in better growth and immune status of L. vannamei.