Olfactory sensitivity to group-specific substances in Atlantic salmon (Salmo salar L.)

The olfactory sensitivity of three groups of Atlantic salmon (Salmo salar L.) toward substances emanating from their own groups was studied. Thresholds were determined by electrophysiological recordings of the induced waves from the medial and lateral part of the olfactory bulb surface. The intestine contained more potent olfactory substances on a gram per liter basis than skin mucus, urine, or amino acids. Chemical fractions were obtained from a parallel study on the nature of the naturally occurring substances by Stabell et al. (1982). A retarded fraction from chromatography on a Sephadex G-25 column contained the most potent material. The most potent fractions of the intestinal content evoked responses mainly in the medial part of the olfactory bulb, whereas the lateral part responded to amino acids. The results suggest that all salmon smolts of the waterways contribute to an odor trail in the coastal currents, thus facilitating the odor-dependent migration of the mature salmon.