Steroid glucuronides of the seminal vesicle as olfactory stimuli in African catfish, Clarias gariepinus

Abstract

Electrical responses were obtained from the olfactory epithelium (electro-olfactogram, EOG) and from the olfactory tract of female African catfish. The EOG response of females to holding water of males depends on the presence and the size of the male's seminal vesicle. Male catfish thus appeared to release odorants originating from the seminal vesicle. The fluid from this exocrine gland is a highly stimulatory odorant because it contains steroid glucuronides. Higher levels of steroid glucuronides in the seminal vesicle fluid of feral spawning males makes the fluid more potent as an olfactory stimulus, whereas removal of the glucuronides diminished the response. Ovulation did not affect the sensitivity to these complex mixtures of glucuronides in the seminal vesicle fluid. The olfactory epithelium of females also responded to solutions of individual synthetic steroid glucuronides. Of the glucuronides tested, 5β-pregnane-3α,17α-diol-20-one-3α-glucuronide was the most potent odorant. It had a detection threshold of approximately 10 −11 M. Thresholds for the other glucuronides ranged between 10 −9 and 10 −6 M. The present data demonstrate the importance of seminal vesicle steroid glucuronides as olfactory cues.