Prostaglandin-Induced Female Spawning Behavior in Goldfish (Carassius auratus) Appears Independent of Ovarian Influence

Abstract

This study was conducted to determine whether prostaglandin f2a (PGF-induced spawning behavior in female goldfish (Carassius auratus) is influenced by sex steroids or by the stage of ovarian development (assessed by gonadosomatic index (GSI), ovary weight expressed as a percentage of body weight). In two groups of intact females with GSI values ranging from 0.2 to 16.6% (Experiment I) and 0.6 to 12.7% (Experiment 5), respectively, there was a significant positive correlation between PGF-induced spawning behavior and GSI; however, within either the previtellogenic fish (GSI < 2.5%) or vitellogenic fish (GSI > 2.5%) of either experiment, the correlation between PGF-induced spawning and GSI was not significant. In one ovariectomy experiment, PGF-induced spawning behavior in ovariectomized fish remained equivalent to that of intact and sham fish between 3 and 13 weeks postsurgery. In a second ovariectomy experiment, ovariectomy did not decrease PGF-induced spawning of ovariectomized fish below presurgery levels, but did result in postsurgery spawning that was significantly less than that of intact and sham fish. At 4 weeks postovariectomy, PGF-induced spawning in females that had received blank silastic implants at surgery was no different from spawning of ovariectomized females implanted with either testosterone or 17βestradiol. PGF-induced spawning also was unaffected by injection of the oocyte maturation-inducing steroid 17α, 20β-dihydroxy-4-pregnen-3-one 16 hr before PGF injection. Together the results indicate that factors associated with ovarian development have only minor influence at most on PGF-induced female spawning behavior, and support earlier proposals that female sex behaviors in externally fertilizing when vertebrates are regulated not by ovarian steroids but by prostaglandins synthesized when ovulated oocytes are in the reproductive tract.