Transient Increase in Chloride Cell Number and Heat Shock Protein Expression (hsp70) in Brown Trout (Salmo trutta fario) Exposed to Sudden Temperature Elevation

The native cold-adapted brown trout (Salmo trutta fario) is often the subject of biomonitoring field studies. Groups of trout were exposed to a sudden temperature rise, from 8 degrees C to 19 degrees C for two hours, and thereafter set back to 8 degrees C. Gill samples of control animals, of fish after the exposure period, and after 24 and 48 hours of recovery at a temperature of 8 degrees C were examined histologically, immunohistochemically, electron microscopically, and by Western blot analysis. By means of immunohistochemistry and electron microscopy, an increase of chloride cells was observed after the temperature elevation. During the recovery period the number of chloride cells decreased. Western blot analysis for stress proteins (hsp70), widely used as a biomarker for environmental stress, was performed from skin and gill. Whereas in the gill both isoforms, the constitutive and the heat inducible form, of hsp70 were detected in all groups, in the skin the control animals only showed the constitutive form. After two hours of exposure both isoforms were visible. An increased expression of hsp70 could be demonstrated in both organs after the exposure. Comparison of the hsp70 values between gill and skin showed tissue-specific differences during the recovery period. In the gill hsp70 rapidly decreased, while in the skin the level remained elevated over the whole observation period. When hsp70 is used as a biomarker in field studies, the fast and organ-specific reaction in the gill and skin of brown trout has to be taken into consideration.