THE EFFECTS OF EARLY CHRONIC EXPOSURE TO SUBLETHAL COPPER ON THE OLFACTORY DISCRIMINATION OF RAINBOW-TROUT, ONCORHYNCHUS-MYKISS

The impact of a long-term sublethal copper exposure on the olfactory discrimination performance was examined in rainbow trout, Oncorhynchus mykiss. Two fish groups, one from the 14th day post-fertilization and the other from hatching, were exposed continuously to 22-mu-g Cu+2.1(-1) for 41 and 37 weeks, respectively. Preference/avoidance responses to different odor conditions (own rearing water/well water; own rearing water/heterospecific water) were evaluated during the 8th month after hatching. The 2 odor conditions appear reliable criteria to evaluate the fish discrimination ability. When controls were given a choice between own rearing water against either well water or heterospecific water, they significantly preferred their own rearing water, whereas both copper-exposed groups showed no preference. The behavioral response of exposed fish indicates impairment of their olfactory discrimination ability; however, it cannot be determined if this reflects a loss of olfactory sensitivity or an olfactory hyposensitivity. Behavioral tests performed 2 and 10 weeks after removal of copper, showed some functional recovery of the olfactory discrimination ability which could be related to the renewal property of olfactory receptor cells. Results demonstrate that a long-term sublethal exposure to copper, as it commonly occurs in the 'natural' condition, may result in olfactory dysfunction with potential impacts on fish survival and reproduction.