ACUTE OLFACTORY SENSITIVITY TO PROSTAGLANDINS BUT NOT TO GONADAL-STEROIDS IN 2 SYMPATRIC SPECIES OF CATOSTOMUS (PISCES, CYPRINIFORMES)

The discovery that released hormones (steroids and prostaglandins) and their metabolites function as potent pheromones in some fishes provides an opportunity to determine whether these chemically identified pheromones are species specific. As a first step in studying this complex issue, we used an extracellular electrophysiological recording technique (electro-olfactogram) to investigate the olfactory sensitivity of two sympatrically spawning catostomid species (white sucker, Catostomus commersoni, and longnose sucker, Catostomus catostomus; Cypriniformes: Catostomidae) to steroids and prostaglandins that might function as sex pheromones. Both species were acutely sensitive to F-series prostaglandins, particularly prostaglandin-F2alpha and its metabolite 15-ketoprostaglandin-F2alpha, but exhibited no olfactory responses to free or conjugated gonadal steroids. The data from tests of olfactory sensitivity to a range of gonadal steroids, though negative, provide preliminary evidence that maturational steroid hormones do not function as pheromones in catostomids as they do in other cypriniform fishes. We were unable to detect species differences in receptor-level olfactory sensitivity to hormones or hormone metabolites, although we cannot discount possible differences at other levels of the olfactory system.