Investigating the effect of ammonia caused by overcrowding on gill tissue pathology and immune system in Asian sea bass

Abstract

Introduction: Ammonia is known as a toxic substance for aquatic organisms, which can be derived from various sources, including agricultural runoff, sewage, and as a waste product from the catabolism of amino acids and proteins by aquatic organisms or resident microorganisms in water. Excessive levels of ammonia can lead to toxicity and stress. Another important issue in aquaculture is the high density of cultured fish in ponds, which itself acts as a limiting factor in the development of aquaculture and increases water ammonia and stress. The present study was conducted to investigate the effect of these two factors on the cultivation of Asian sea bass under high density in freshwater. Materials & methods: For this purpose, 375 pieces of Asian sea bass were randomly assigned to 5 groups with 3 replicates at densities of 6 (G1), 8 (G2), 10 (G3), 12 (G4), and 14 (G5) gr/L, and the daily ammonia concentration was measured for a period of 60 days. At the end of the cultivation period, in addition to innate immune system, and evaluation Histopathological of gills tissue were measured. In the G1, G2, and G3, following 30 days, no pathological lesions were observed in the examined gills. Results: However, in the G4, 50% of the samples exhibited lesions like hyperemia and bleeding, while in the G5 with the highest density, 75% of the gills showed lesions such as hyperemia and bleeding. After 60 days, the G1 and G2 remained free of any pathological lesions. Nevertheless, in the G3 and G4, 16/6% of the gills displayed lesions, and in the G5, 33/3% exhibited lesions such as hyperemia and adhesion of secondary lamellae. The results of the present study showed that complement and lysozyme activity on day 30 had a significant difference between the groups (P<0.05), so the G5 showed the highest value. Also, the highest activity of reduction Nitro blue tetrazolium (NBT) and myeloperoxidase was observed in the G1 and G3 was observed in respectively (P<0.05). However, no significant difference was observed in antitrypsin during the day. On the 60th day, a significant decrease in the amount of complement, lysozyme and antitrypsin was observed in the G5 (P<0.05), also the amount of myeloperoxidase in the G1 and the amount of NBT in the G5 had the highest amount (P<0.05). Regarding other parameters such as total protein activity, globulin and bactericidal effect, a significant difference was obtained between the groups on day 30 and 60 (P<0.05). The present study showed that the density of 12 (G4) and 14 (G5) gr/L in the first 30 days of the experiment, histopathological lesions were observed in the gill tissue, but this type of fish in the mentioned densities is in line with the conditions of increased ammonia water, on the 60th day, the reduction of lesions in the gill tissue was observed, and these responses were adjusted in line with the adaptability of the fish to the prevailing stress conditions. Conclusion: According to the results of Immune system and histopathological investigations, the concentration of 8 gr/L (G2) is usually enough to ensure the healthy growth of fish during the culture period (long term) and at the same time, it prevents problems such as stress and diseases.