Morphological and functional characteristics of the olfactory and gustatory organs of three Salvelinus species

Abstract

Morphological features and response characteristics of the olfactory and gustatory organs were studied in three char species, Arctic char (Salvelinus alpinus), brook char (S. fontinalis), and lake char (S. namaycush). In brook, lake, and Norwegian-stock Arctic chars the olfactory rosette consisted of 12–16 primary olfactory lamellae radiating from the rostro-caudally oriented raphe, with the secondary folding typical of salmonids. Nauyuk-stock Arctic char had fewer (7–9) olfactory lamellae without secondary folding. Electro-olfactogram response characteristics to L-cysteine, L-arginine, and L-glutamate, representing neutral, basic and acidic amino acids, respectively, were similar, with threshold concentrations of 10−9–10−8 M. Structure–activity relationship studies showed that the amino acid spectrum for Arctic char differed from those of brook and lake chars. Most characteristic was that esterification of the carboxyl group of L-arginine enhanced its effectiveness. The taste buds were generally distributed in rows oriented anterior–posterior in the palate. Each species showed distinct distribution patterns, and the highest densities (up to 40/mm2) of palatal taste buds were counted in brook char. The palatine nerve of the three species responded specifically to L-proline, hydroxy-L-proline, and L-alanine. Adaptation to L-proline eliminated responses to hydroxy-L-proline and L-alanine. No response was registered to betaine, one of the most potent gustatory stimulants for teleosts. Tetrodotoxin, quinine, and strychnine were potent gustatory stimulants in the three species. The detection threshold for tetrodotoxin was lower than for L-proline in Arctic char. We conclude that the three char species have only one main palatine gustatory amino acid receptor, that for L-proline.