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[Display omitted] • Niacin deficiency decreased the growth performance of fish. • Niacin deficiency affected muscle amino acid and fatty acid compositions of fish. • Niacin deficiency exerted negative impacts on flesh physicochemical properties. • Niacin deficiency may quicken flesh pH drop by promoting glycolysis. • Niacin deficiency impaired mitochondrial homeostasis. Energy metabolism exerts profound impacts on flesh quality. Niacin can be transformed into nicotinamide adenine dinucleotide (NAD), which is indispensable to energy metabolism. To investigate whether niacin deficiency could affect energy metabolism and flesh quality, six diets with graded levels of 0.49, 9.30, 21.30, 33.30, 45.30 and 57.30 mg/kg niacin were fed to grass carp (Ctenopharyngodon idella) for 63 days. The results showed that niacin deficiency declined flesh quality by changing amino acid and fatty acid profiles, decreasing shear force, increasing cooking loss and accelerating pH decline. The accelerated pH decline might be associated with enhanced glycolysis as evident by increased hexokinase (HK), pyruvate kinase (PK) and lactic dehydrogenase (LDH) activities, and mitochondrial dysfunction as evident by destroyed mitochondrial morphology, impaired respiratory chain complex I and antioxidant ability. Based on PWG and cooking loss, the niacin requirements for sub-adult grass carp were 31.95 mg/kg and 29.66 mg/kg diet, respectively. [ABSTRACT FROM AUTHOR]

Growth performance, flesh quality, antioxidant status and antioxidant-related signalling molecule expression in the muscle of young grass carp, which were fed graded levels of arginine (6.9–24.5 g/kg diet) for eight weeks, were investigated. Muscle protein, lipid and nitric oxide contents, shear force, hydroxyproline concentration, and pH were significantly improved by appropriate arginine. Cooking loss, lactate content, cathepsins activities, malondialdehyde and protein carbonyl contents exhibited an opposite tendency. Additionally, optimum arginine significantly enhanced glutathione content and the activities and gene expression of copper/zinc superoxide dismutase, catalase and glutathione peroxidase in muscle. Moreover, the expression levels of glutamate–cysteine ligase, target of rapamycin, ribosome protein S6 kinase 1, casein kinase 2 and NF-E2-related factor 2 in muscle were significantly elevated by appropriate arginine. However, optimum arginine significantly decreased Kelch-like ECH-associated protein 1 mRNA levels in muscle. In conclusion, arginine improved the flesh quality and muscle antioxidant capacity and regulated antioxidant-related signalling molecule expression. [ABSTRACT FROM AUTHOR]

Flesh quality, muscle antioxidant status and related signalling molecule expressions were investigated in young grass carp fed six levels of tryptophan (Trp) for 8 weeks. The results indicated that fish fed 0.7 (deficiency) and 6.1 g Trp g/kg (excess) diets exhibited lower muscle water-holding capacity, tenderness, cathepsin activity, protein levels, lipids and collagen contents. Optimal Trp reversed these negative effects, which were related to enhanced glutathione (GSH) content and glutathione peroxidase (GPx) activities regulated at gene transcription levels, rather than to superoxide dismutase (SOD) or catalase (CAT). The expression of signalling molecules [Kelch-like ECH-associated protein 1, target of rapamycin (TOR) and ribosomal S6 protein kinase 1] involved in the NF-E2-related factor 2 (Nrf2) pathway revealed a potential method of Trp-enhanced antioxidant defence. Collectively, the present study indicated that appropriate Trp levels improved flesh quality partly related to the enhancement of antioxidant ability through Nrf2 and TOR signalling. [ABSTRACT FROM AUTHOR]