MORPHOFUNCTIONAL ALTERATIONS IN THE OLFACTORY SYSTEM OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) AND POSSIBLE ACCLIMATION IN RESPONSE TO LONG-LASTING EXPOSURE TO LOW COPPER LEVELS

Morpho-functional changes in the olfactory system of Oncorhynchus mykiss were investigated at different times during a 40-week exposure to either 20 mu g Cu-2+/l (20-mu g group) or 40 mu g Cu-2+/l (40-mu g group), Histopathological alterations in the olfactory epithelium of the 20-mu g group were moderate, whereas those in the 40-mu g group were more severe and intensified with time exposure, The 20-mu g group exhibited some olfactory discrimination ability but presented higher sensitivity thresholds than controls. The 40 mu g group became unresponsive with time, even to a water inflow 4 times more odor concentrated, The time frame for morpho-functional recovery after returning to well water was dose dependent, Morpho-functional alterations in response to a 20 mu g Cu-2+/l exposure appeared less important and the functional recovery shorter in adults compared to what has been previously observed in younger fish. Fish acclimation in conditions of long-lasting exposure to each copper dose is discussed.