Olfactory sensitivity to bile acids in salmonid fishes

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Abstract
Monopolar DC-recordings were made simultaneously from 2 positions on the olfactory bulb of chars (Salmo alpinus L.) and graylings (Thymallus thymallus L.) using bile acids and amino acids as olfactory stimulants. The bile acids induced responses with characteristic spatial differences from those of the amino acids. The distribution of responses to bile acids indicated a neuronal activity in the medial part of the bulb. Amino acids elicit responses in the lateral part of the bulb. Taurine conjugated bile acids were up to 1000 times more potent as olfactory stimuli than methionine. Olfactory receptors may be of 2 types, one responding to bile acids, the other to amino acids. 3-.alpha.-Hydroxysteroids are released from the fish into the water in quantities that suffice for detection by their olfactory system. The odorant potency of the bile acids, their evolutionary history and variability and their renowned adherent properties made them interesting candidates for specific signals in the aquatic environment.