Effects of Ala-Gln on growth, biochemical indicators and stress-related gene expression of largemouth bass (Micropterus salmoides) under dual stress of flow rate and density

The experiment focused on the study aimed to investigate the effects of adding alanyl-glutamine (Ala-Gln) to the feed on the growth, serum biochemical parameters, and the mRNA expression levels of stress-related genes in largemouth bass (Micropterus salmoides) under dual stress conditions of density and flow rate. The fish were divided into three groups: control group, dual stress group and dual stress with 0.9 % Ala-Gln addition group, and underwent a 60 day aquaculture experiment. The data showed that final weight, average weight gain rate, specific growth rate and feed efficiency of largemouth bass significantly decreased under dual stress (P < 0.05). At the same time, the levels of glucose and malondialdehyde (MAD), the activities of aspartate aminotransferase (AST) and alanine transaminase (ALT) in serum increased significantly under dual stress, while the total antioxidant capacity and serum lysozyme activity decreased significantly (P < 0.05). Moreover, the mRNA expression of growth hormone (GH), insulin-like growth factor-Ⅰ(IGF-I), nuclear factor kappa-B (NF-κB), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), nuclear transcription factor E2 related factor 2 (Nrf2), catalase (CAT), superoxide dismutase (SOD), Caspase 3, Caspase 8 and B-cell lymphoma-2 (Bcl2) genes all decreased significantly, the mRNA expression of HSP 70, HSP 90, interleukin-10 (IL-10), I-kappa-B-alpha (IkBα), kelch-1ike ECH- associated protein 1 (Keap1) and bcl2-associated X (Bax) genes all increased significantly (P < 0.05). However, the growth performance, serum biochemical indexes and mRNA expression of most genes in largemouth bass showed a correction trend after Ala-Gln addition, but still did not reach the level of control group. These results showed that dual stress of density and flow rate reduced growth and serum biochemical parameters in largemouth bass and increased the adverse expression of stress-related genes, while exogenous addition of Ala-Glu could somewhat ameliorate the negative effects of dual stress on largemouth bass.