Introduction: Seabass is a euryhaline and catadromous species. When fish are exposed to environmental stress, anatomical changes occur in their bodies, and if these changes are not corrected or compensated, the body becomes weak and loses its ability to deal with other stressful factors. Therefore, the aim of this study is to investigate the effects of different salinities without adaptation on blood electrolytes and the structure of gill and kidney tissues in Asian seabass (Lates calcarifer).
Materials and methods: This experiment was conducted at the Persian Gulf Research Institute located in the Persian Gulf University, Bushehr. A number of 180 Asian seabass fry were adapted to laboratory conditions and concentrated food for 14 days before starting the experiment. To conduct the present experiment, 4 treatments with 3 replications were considered. The fishes were randomly selected and distributed in 12 tanks with a volume of 300 liters of water and a density of 15 pieces of fish in each tank. The length of the test period was 120 hours. The desired salinities were obtained by diluting sea water (50 ppt) with fresh water. The experimental treatment included the treatment 1 (fresh water), treatment 2 (treatment with salinity of 15 g/L), treatment 3 (treatment with salinity of 35 g/L) and treatment 4 (treatment with salinity of 50 g/L).
Results: The results of the present study showed that different salinities without adaptation in the amount of osmolality, sodium, potassium and chlorine ions in the blood of Asian seabass fish cause significant changes in different hours of the experiment (P<0/05). Lesions such as hypertrophy of chloride cells, telangiectasia at the tips of secondary lamellae, epithelial necrosis and adhesion of lamellae were observed in the gill tissue. Also, in the kidney tissue, lesions such as an increase in the concentration of melano-macrophages, an enlargement of Bowman's capsule, an increase in the space in the center of the glomerulus, and