Dietary DL‐methionyl‐DL‐methionine supplementation could improve growth performance under low fishmeal strategies by modulating TOR signalling pathway of Litopenaeus vannamei

Abstract

An 8-week feeding trial was conducted to investigate the effects of DL-methionyl-DL-methionine (Met-Met) supplementation in different fishmeal levels on growth performance, antioxidant and immune response of juvenile Pacific white shrimp, Litopenaeus vannamei. Eight isonitrogenous and isolipidic experimental diets were formulated to meet the nutrient requirements of Pacific white shrimp. The supplemental amount of fishmeal in diets without essential amino acid supplementation are 200 g/kg (F20), 100 g/kg (F10), 50 g/kg (F5) and 0 g/kg (F0), and with essential amino acid supplementation are 200 g/kg (M20), 100 g/kg (M10) 50 g/kg (M5) and 0 g/kg (M0) respectively. The results indicated that shrimp fed the F5 and F0 diets had significantly lower final body weight (FBW), per cent weight gain (PWG), specific growth rate (SGR) and higher feed conversion ratio (FCR) compared with those fed the F20 diet (p < .05). Glucose (GLU), triacylglycerol (TG) and cholesterol (CHO) concentration in haemolymph significantly decreased with fishmeal supplementation decreasing from 200 g/kg to 0 g/kg (p < .05). Met-Met supplementation in low fishmeal diets significantly reduced the content of malondialdehyde (MDA), increased the activities of acid phosphatase (ACP) and lysozyme (LZM) in hepatopancreas, as well as increasing the activity of total antioxidant capacity (T-AOC) in haemolymph (p < .05). Meanwhile, shrimp fed M5 and M0 diets had significant upregulation of gene expression of acp, lzm (immune-related), RagC and s6k (TOR signalling pathway‑related) in hepatopancreas (p < .05). In conclusion, the present study demonstrated that dietary Met-Met supplementation could improve the growth performance and the abilities of antioxidant and non-specific immunity of Pacific white shrimp by reducing MDA concentration, increasing T-AOC, ACP and LZM activities, and upregulating gene expression level of immune (acp and lzm) and TOR signalling pathway (RagC, and s6k). Moreover, Pacific white shrimp fed low fishmeal diets had the positive response of well-balanced amino acid, and the results will provide further insight into the possibility of reducing fishmeal content in the commercial feed of shrimp.