Immunological, hematological, and histological responses in blood, spleen and gill of Salmo caspius juveniles exposed in different water temperatures

Caspian brown trout, Salmo caspius, were subject to five temperatures (5°C, 8°C, 20°C, 25°C, and 28°C) for two durations 12 and 24 hours. The fish were maintained for 48 hours at a water temperature of 9-10°C to acclimatize.The water temperature was changed gradually at a rate of 2°C per hour to the respective temperatures. Exposure to temperatures of 25 and 28°C resulted in loss of all fish. Red blood cell, hemoglobin concentration, and hematocrit were decreased at 5°C compared to control (8°C) and 20°C in duration of 12h. Temperature tension did not affect the mean cell volume and mean cell hemoglobin value during the 12 and 24h duration (p >0.05). Neutrophils percentage was  significantly higher at 5°C and 20°C, but the most percentage of lymphocytes was noted in the control group. Cortisol, glucose, and lactate values elevated in both periods when water temperature decreased to 5°C compare to the control and 20°C groups (p <0.05). The levels of albumin and total protein in the duration of 12h at 20°C were significantly higher than control and 5°C, but this trend was not seen in the exposure of 24h (p <0.05). The lysozyme activity and immunoglobin M were affected by varying temperatures (p <0.05), and highest levels were observed in control groups.  Most histopathological changes in gill, such as epithelial hypertrophy, curling of lamella, and necrosis of the epithelial cell were observed at 20°C; whereasthese were less affected at 5°C and 8°C.  Lowest hemorrhages in the spleen and lowest size of sinusoids were observed in 8°C and 5°C treatments respectively. Overall, temperature variation had a superior impact on gills than spleen. Taken together, the results of the present study showed that sudden variation beyond the optimum temperature leads to physiological and pathological changes.