Behavioral, biochemical, and electrophysiological studies suggest that the trihydroxylated progestin steroid, 4-pregnen-17,20β,21-triol-3-one (20β-S) stimulates oocyte maturation and pheromone release in the Eurasian ruffe, a freshwater percid fish. Behavioral observations found that female ruffe undergoing oocyte maturation (OM) release a pheromonal cue that stimulates swimming activity and social interactions among conspecific males. Neither vitellogenic nor ovulated females released the cue. Pheromone production was directly associated with elevated plasma levels of 20β-S in maturing female ruffe which in vitro incubation suggested to be a possible maturation-inducing hormone (MIH) in this species along with 4-pregnen-17,20β-diol-3-one (17,20βP). However, neither of these steroids appear to be the pheromone because electrophysiological and behavioral studies found them to lack olfactory (EOG) and behavioral activity. Instead, studies of the odor of steroid-injected fish suggest the pheromone is a metabolite of 20β-S. In particular, inter-peritoneal injection of 20β-S (but not 17,20βP) consistently induced release of a urinary cue with strong behavioral activity. The pheromone may be a highly polar and novel metabolite because it could not be extracted using octadecylsilane resin (C18) which has proven effective for other teleost hormonal pheromones.
- Maturation-inducing hormone
- Oocyte maturation