Effects of dietary glycine administration on biochemical responses to ammonia toxicity in common carp, Cyprinus carpio

Abstract

The benefits of dietary glycine supplementation were investigated in common carp, Cyprinus carpio, following an acute ammonia challenge. Fish were fed diets supplemented with glycine (0, 2.5, 5 and 10 g/kg; named C, 2.5G, 5G and 10G, respectively) for 3 weeks, followed by 3-h exposure to 0.5 mg/L unionized ammonia nitrogen. Plasma immunoglobulin levels showed no changes in relation to ammonia challenge or dietary glycine supplementation. Dietary glycine significantly decreased plasma glucose, but increased plasma total antioxidant capacity (TAC) and glutathione (GSH). Ammonia exposure significantly increased plasma glucose and alternative complement, but decreased plasma GSH and TAC levels. Dietary glycine and ammonia exposure induced interaction effects on plasma ammonia, urea, cortisol, lysozyme, alanine aminotransferase (ALT), aspartate aminotransferase (AST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and malondialdehyde (MDA). Before ammonia exposure, glycine administration significantly decreased plasma ammonia and urea; after ammonia exposure, glycine supplementation significantly mitigated hyperammonaemia, but stimulated uraemia. Dietary glycine induced no changes in plasma cortisol before ammonia challenge, but decreased it after the ammonia challenge. Dietary glycine had no significant effects on ALT, AST, SOD and MDA, decreased CAT, but increased GPx and GST, before ammonia exposure. Moreover, dietary glycine mitigated the ammonia-induced elevations in ALT, AST, SOD, CAT, GPx, GST and MDA. Among the treatments, 10G exhibited the lowest ammonia-induced changes in the tested parameters; thus, it is recommended to use 10 g glycine per kg diet for 3 weeks to mitigate ammonia-induced stress, oxidative stress and hepatic damages in common carp.