Olfactory inhibition and recovery in chum salmon (Oncorhynchus keta) following copper exposure

Abstract

Copper can be an effective hatchery treatment to control certain parasitic and fungal infections in salmonids, yet it is also highly toxic to the fish's olfactory system. Numerous reports have described the early inhibitory impacts of copper on fish olfaction, but very few have addressed processes of recovery. Here we show that the chum salmon (Oncorhynchus keta) olfactory system can recover from short-term (4 h) exposures to copper (3–58 µg·L–1) within 1 day, as indicated by electro-olfactogram (EOG) recordings. Recovery followed initial EOG reductions of up to 88%. We also applied a novel cytophysiological approach to monitor changes in the olfactory receptor cells using a fluorescent styryl dye, AM1-43. Copper's influence on the number of receptor cells that labelled with the dye was biphasic, initially increasing the number at the two lowest copper concentrations (3 and 8 µg·L–1) and decreasing the number at the two highest concentrations (24 and 58 µg·L–1). Changes in the ability of olfactory receptor neurons to internalize the dye were monitored up to 10 days in fish recovering from copper exposure.