Sub-chronic ammonia exposure induced growth inhibition, muscle oxidative stress, flesh quality deterioration, and metabolomic shifts of grass carp (Ctenopharyngodon idellus)

This study investigated the effects of sub-chronic ammonia exposure on the growth performance, nutrient composition, metabolic profile, and meat quality of grass carp (Ctenopharyngodon idellus). Compared to the control, sub-chronic ammonia stress reduced protein synthesis, lowered muscle crude protein content and myofiber diameter, resulting in growth inhibition. Ammonia stress also triggered reactive oxygen species (ROS) accumulation and oxidative stress attributable to diminished antioxidant capacity. Furthermore, ammonia stress increased lactate and glucose levels, as well as glycolytic potential, while decreasing pH and water-holding capacity. Metabolomic analysis identified key metabolites and pathways underlying these changes, encompassing amino acid metabolism, lipid metabolism, choline metabolism, and nucleotide metabolism. Specifically, ammonia exposure reduced the sensory and nutritional attributes of grass carp muscle, as evidenced by decreased levels of flavor amino acids, total amino acids, n-3 polyunsaturated fatty acids, and umami nucleotides. Correlation analysis further revealed significant associations between differential metabolites and meat quality alterations. This study provides new insights into the impact of ammonia stress on fish growth and meat quality, and establishes a theoretical basis for maintaining fish muscle quality under environmental stress.