Influence of the olfactory sense upon smolt transformation in salmonid fishes.

The effect of olfactory deprivation on the process of smolt transformation in Atlantic salmon (Salmo salar L.) was investigated. Salmon parr were rendered anosmic by heat-cauterizing in November, and, together with controls, size, purine deposition (silvering), and mortality were monitored throughout spring in individuals within sibling groups. In May the fish were exposed to seawater (3.2% salinity) to determine levels of smoking in anosmic fish compared with control fish. Olfactory deprivation was found to induce a negative effect on survival in both anosmic fish as well as controls when reared within the same rearing tank. A 54% survival was metered in anosmic fish as opposed to only 26% survival in control fish during the experimental period. The low survival rates observed are suggested to result from abnormal behavior in anosmic fish due to lack of proper olfactory stimuli. Within each strain, the anosmic fish were found shorter and displayed less-silvering than their control fish at the end of the experimental period. Further, since control fish could withstand salinity exposure longer than anosmic fish, smolting is suggested to have been retarded among the anosmic fish. Olfactory influence on smolt transformation may be caused by conspecific pheromones secreted for the purpose of mediating effects of life-history patterns in salmonid fishes.