Chinook Salmon (oncorhynchus Tshawytscha) and Rainbow Trout (oncorhynchus Mykiss) Exposed to Copper: Neurophysiological and Histological Effects on the Olfactory System

Olfactory epithelial structure and olfactory bulb neurophysiological responses were measured in chinook salmon and rainbow trout in response to 25 to 300 mg copper (Cu)/L. Using confocal laser scanning microscopy, the number of olfactory receptors was significantly reduced in chinook salmon exposed to $50 mg Cu/L and in rainbow trout exposed to $200 mg Cu/L for 1 h. The number of receptors was significantly reduced in both species following exposure to 25 mg Cu/L for 4 h. Transmission electron microscopy of olfactory epithelial tissue indicated that the loss of receptors was from cellular necrosis. Olfactory bulb electroencephalogram (EEG) responses to 1023 M L-serine were initially reduced by all Cu concentrations but were virtually eliminated in chinook salmon exposed to $50 mg Cu/L and in rainbow trout exposed to $200 mg Cu/L within 1 h of exposure. Following Cu exposure, EEG response recovery rates were slower in fish exposed to higher Cu concentrations. The higher sensitivity of the chinook salmon olfactory system to Cu-induced histological damage and neurophysiological impairment parallels the relative species sensitivity observed in behavioral avoidance experiments. This difference in species sensitivity may reduce the survival and reproductive potential of chinook salmon compared with that of rainbow trout in Cu-contaminated waters. Keywords—Copper Chinook salmon Rainbow trout Olfactory bulb electroencephalogram Olfactory histology