Gonadal steroidogenesis and the possible role of steroid glucuronides as sex pheromones in two species of teleosts

Abstract

In general, female zebrafish,Brachydanio rerio, ovulate only in the presence of males. The stimulant must be pheromonal as even male holding water is capable of inducing ovulation. After ovulation the mating phase begins. During this phase the male follows the female and oviposition as well as fertilization takes place. Both the ovulation and the mating are controlled by pheromones synthesized by the gonads. Ovulation can be induced by testicular homogenates. After the lipid material has been extracted from the testicular homogenates, the remaining aqueous phase can still induce ovulation. However, when the aqueous phase is treated with the enzymeβ-glucuronidase, it loses the ability to induce ovulation. This is an indication that glucuronides, probably steroid glucuronides, are the compounds responsible.During the mating phase, ovulated female zebrafish become attractive to males. It was found that, after ovulation, ovarian extracts contain the compounds responsible for attracting males. The attractant consists of a mixture of steroid glucuronides.After incubation of the gonads with(3)H-precursors seven steroid glucuronides have been identified in the testis and five in the ovary.Under fish culture conditions the African catfish,Clarias gariepinus, can produce postivitellogenic oocytes throughout the year. However, in capitivity neither males nor females spawn. In female catfish maturation and ovulation can be induced by treatment with gonadotropins. It might be possible that, analogous to the zebrafish, some reproductive processes in the catfish have to be induced by pheromones. It has been demonstrated that pheromonal compounds released by the seminal vesicles are involved in the attraction of female conspecifics. The steroid glucuronide synthesizing capability of the testes and the seminal vesicles of the male catfish are examined, as well as that of the ovary before and after ovulation of the female catfish. Both testes and seminal vesicles appear to be capable of steroid biosynthesis but only the latter synthesizes steroid glucuronides. Six of these conjugates have been isolated and identified. In the female catfish the ovaries are capable of synthesizing seven steroid glucuronides, but only after ovulation.

The biosynthesis of steroid glucuronides in the testis of the zebrafish, Brachydanio rerio, and their pheromonal function as ovulation inducers

“…In zebrafish, Brachydanio verio, intersexual attraction can be caused by extracts of postovulatory zebrafish ovaries (van den Hurk and Lambert 1983;Lambert et al, 1986) and ovulation can be induced by male holding water (Chen and Martinich, 1975). Little is known about the biochemical nature of these fish pheromones.…”

The skin of the male African catfish, Clarias gariepinus: A source of steroid glucuronides

“…In the African catfish steroid glucuronides can act as pheromones (Lambert et al, 1986;Resink et al, 1987). The present results indicate that the skin, and in particular its epithelial cells, is capable of synthesizing steroid glucuronides.…”

“…However, the possibility of steroid glucuronides, formed in the skin, playing a significant role as sex pheromones cannot be ruled out. In the African catfish, steroid glucuronide fractions, obtained from seminal vesicles and ovaries, possess pheromonal functions (Lambert et al, 1986;Resink et al, 1987). Pheromonal properties of steroid glucuronides were also demonstrated in zebrafish, B. rerio (Van den Hurk and Lambert, 1983) and in G. *jozo (Colombo et al, 1980).…”

Steroidogenesis in the testes and seminal vesicles of spawning and non-spawning African catfish, Clarias gariepinus

“…Recent experiments by Resink et al (198713) -see also Lambert et al (1986) and Van Oordt (1986) -have shown that the fluid produced by the seminal vesicles of African catfish is involved in the attraction of females after ovulation. Preliminary experiments have made it possible to identify three steroid glucuronides in this fluid, namely 5j?-pregnane-3cu,l7a-diol-20-one-glucuronide, 5P-androstane-3a,l7/?-diol-glucuronide and etiocholanolone-glucuronide ( Schoonen, in preparation).…”

“…Steroid glucuronides of testicular origin have been described for the teleosts Gobius paganellus (Colombo et al, 1970)) G. jozo (Colombo et al, 1977), the rainbow trout (Hews and Kime, 1978)) the goldfish (Kime, 1980)) Sarotherodon mossambicus (Kime and Hyder, 1983) and the zebrafish, Brachydanio rerio (Lambert et al, 1986;Van Oordt, 1986;Van Den Hurk et al, 1987b). In G. jozo etiocholanolone-glucuronide attracts ovulated females (Colombo et al, 1980(Colombo et al, , 1982.…”