Endocrinology of teleost reproduction: A testicular steroid pheromone in the black goby,Gobius jozoL.

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Abstract
The male black goby, Gobius jozo, is known to possess a large mesorchial gland which synthesizes large amounts of 5β-reduced androgens conjugates, especially etiocholanolone glucuronide. When gravid females releasing eggs on stripping were exposed singly to this steroid in a tank monitored through a closed television circuit, most of them manifested appetitive behaviour with negative kinesis towards the steroid source and were stimulated to lay their eggs. The steroid stimulus was effective in low concentration (below 2μM), in still water, and in the absence of sensorial reinforcements by a male partner. Females were little or not responsive outside in the interval between ovulation and oviposition. The pheromonal system of the black goby resembles that of the pig where the smell of the testicular 16-androstenes in the boar's breath induces the mating stance in the estrous sow. Both species are characterized by overdevelopment of the Leydighian compartment, chemical divergence between hormonal and pheromonal androgens and environmental diffusibility of the testicular pheromones. The occurrence of the last-named compounds supports the concept that the evolution of the bioregulatory function of gonadal steroids in vertebrates is aimed at the progressive elongation of the communication channel connecting the steroid-secreting with the steroid-responsive sites in order to reduce gamete wastage for species perpetuation. A three-stage model is proposed describing the expansion of the steroid control function in terms of sequential recruitment of germinal, somatic and pheromonal targets, in this order. It is also suggested that non-nuclear mechanisms of steroid actions may be operative in all the three groups of targets.