Research Article: 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 (۵°C, ۸°C, ۲۰°C, ۲۵°C, and ۲۸°C) for two durations ۱۲ and ۲۴ hours. The fish were maintained for ۴۸ hours at a water temperature of ۹-۱۰°C to acclimatize. The water temperature was changed gradually at a rate of ۲°C per hour to the respective temperatures. Exposure to temperatures of ۲۵ and ۲۸°C resulted in loss of all fish. Red blood cell, hemoglobin concentration, and hematocrit were decreased at ۵°C compared to control (۸°C) and ۲۰°C in duration of ۱۲h. Temperature tension did not affect the mean cell volume and mean cell hemoglobin value during the ۱۲ and ۲۴h duration (p>۰.۰۵). Neutrophils percentage was  significantly higher at ۵°C and ۲۰°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 ۵°C compare to the control and ۲۰°C groups (p<۰.۰۵). The levels of albumin and total protein in the duration of ۱۲h at ۲۰°C were significantly higher than control and ۵°C, but this trend was not seen in the exposure of ۲۴h (p<۰.۰۵). The lysozyme activity and immunoglobin M were affected by varying temperatures (p<۰.۰۵), 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 ۲۰°C; whereas these were less affected at ۵°C and ۸°C.  Lowest hemorrhages in the spleen and lowest size of sinusoids were observed in ۸°C and ۵°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.

Keywords:

Biochemical indices , Gill , immune parameters , Salmo caspius , Temperature stress