Sh. Rezakhani - Department of Fisheries, Bandar abbas Branch, Islamic Azad University, Bandar abbas, Iran
F. Mohammadizadeh - Department of Fisheries, Bandar abbas Branch, Islamic Azad University, Bandar abbas, Iran
H. Khara - Department of Fisheries, Lahijan Branch, Islamic Azad University, Lahijan, Iran, P.O. Box: ۱۶۱۶
A.H. Bahri - Department of Fisheries, Bandar abbas Branch, Islamic Azad University, Bandar abbas, Iran
M. Ahmadnezhad - Inland Water Aquaculture Center, Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Bandar Anzali, Iran, P. O. Box: ۶۱

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.

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