Effects of long-term exposure to ammonia on growth performance, immune response, and body biochemical composition of juvenile ivory shell, Babylonia areolata

Ammonia is one of the most significant environmental pollutants affecting aquatic animals under culture conditions; however, little is known about ammonia toxicity in marine gastropods. In this study, the effects of different total ammonia concentrations (0.0, 2.5, 5.0, 7.5, and 10.0 mg.L-1 NH4Cl) on growth performance, tissue damage, antioxidant capacity, immune function, and body composition were investigated in carnivorous ivory shells (Babylonia areolata) after seven weeks of rearing. The growth performance of ivory shells in the higher ammonia treatments (>= 5.0 mg.L-1) was significantly lower than that of the control group (P < 0.05). Significantly higher mortalities were observed in the 7.5 and 10.0 mg.L-1 ammonia-treated groups than those in the control group (P < 0.05). After ammonia exposure, obvious tissue damage in the gill was observed, whereas almost no differences were observed in the hepatopancreas between the control and ammonia-treated groups. The activities of superoxide dismutase (SOD) and catalase (CAT) in the gill and hepatopancreas decreased with increasing ammonia concentrations. The activities of acid phosphatase (ACP) and alkaline phosphatase (AKP) in the hepatopancreas also significantly decreased when ivory shells were cultured in ammonia (P < 0.05), while these two immune enzymes in the gill reached the highest level in the 2.5 mg.L-1 ammonia-treated group and decreased with the increase of ammonia concentration. The content of malondialdehyde (MDA) and activities of Na+/K+-ATPase (NKA), aspartate transaminase (AST), and alanine transaminase (ALT) increased with an increase in ammonia concentration. The amino acid content in the muscle of the ammonia-treated groups was lower than that in the control group, while almost all amino acid content in the hepatopancreas increased first and then decreased. Furthermore, the composition of polyunsaturated fatty acids (PUFAs) (e.g., C22:5n3 in the muscle; C22:6n3 and C20:5n3 in the hepatopancreas) showed an increasing tendency and then a decreasing tendency with an increase in ammonia concentration. Our study suggested that higher ammonia (>= 5.0 mg.L-1) not only caused a decrease in growth performance, immune and antioxidant-related enzymes, and an increase in mortality, tissue damage, and extra energy metabolism, but also led to significant changes in the nutritional composition of the ivory shell.