Dietary kelp meal (Thallus laminariae) improves the immunity of hybrid snakeheads under ammonia stress

Abstract

This study determined the effect of dietary kelp meal (KM) on metabolism of the hybrid snakeheads (Channa maculatus ♀ × Channa argus ♂), and the spatiotemporal changes in their resistance to ammonia stress, including survival rate, histopathology, biochemical parameters, and the expression of immune-related genes. The experimental diets contained: 0% KM, 5% KM, 10% KM, 15% KM, 15% KM + 5% binder. After eight weeks of feeding, six fish per diet were sampled for metabolic studies, and the remaining fish were placed under ammonia stress at two concentrations (1200 mg/L and 120 mg/L) for 48 h. Our results showed that replacing flour with kelp meal to the diet could alter the activities of some metabolic enzymes and reduced the lethality of hybrid snakeheads under high ammonia exposure. Histopathological results revealed a variety of pathological features in the liver after exposure to ammonia nitrogen. The levels of glutamate dehydrogenase (GDH), glutamine synthetase (GS), superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) showed the trend of first increasing and then decreasing with the decrease of the flour concentration in the diet under high concentration of ammonia stress. Besides, kidneys receive more severe oxidative damage than the liver. Similar results were found in the mRNA abundance of immune-related genes, and the kidney were mostly significantly down-regulated, but feeding moderate amounts of kelp meal can alleviate this damage. The transcriptome analysis showed that kelp meal can affect antigen processing and presentation process by the MHCⅠ signaling pathway mechanism, and thus regulate the immune response of hybrid snakeheads. Our study suggests that adding kelp meal in the diets could improve the ability of hybrid snakeheads to resist ammonia stress and the optimal replacement group is 10% KM group.