The knowledge of fish biology of stress response to unfavourable environmental conditions is of interest for both basic and applied purpose, providing useful information for fish farming and environmental risk assessment. In this study, tilapias (Oreochromis mossambicus), confined in nets inside the tanks for 4 or 5 hrs, were examined for induction of Hsp 70 in various organs by western blotting and for cortisol levels in the blood. In net-confined fish, cortisol, primary stress indicator, was found to consistently increase with differences between 4 and 5 hrs of confinement. Hsp 70 expression, evaluated in striated and cardiac muscle, gill, liver and brain showed fluctuation in confined animals. Indeed, increase or decrease of Hsp 70 expression in stressed fish was modified in organ- and stress duration-dependent manner and subjective fluctuation were minimal. Morphological observations (LM and EM) were carried out on liver, brain and gill from control and stressed animals. In particular, liver underwent major modifications while brain was only slightly modified and gills were unmodified during confinement stress. Taken together our data suggest that Hsp 70 expression could be an indicator of stress state in fish when measured in the significant responsive organs.
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