GONADAL DEVELOPMENT AND ASSOCIATED CHANGES IN PLASMA REPRODUCTIVE STEROIDS IN ENGLISH SOLE, PLEURONECTES VETULUS, FROM PUGET-SOUND, WASHINGTON

Gonadal development, and associated changes in reproductive parameters were investigated in adult female and male English sole (Pleuronectes vetulus) in Puget Sound to provide baseline data for future research on effects of contaminants on reproductive endocrine function in this species. Changes in gonadal histology, gonadosomatic index (GSI), and plasma reproductive steroids (female: 17 beta-estradiol [E2], testoste rone [T]; male: T, 11-ketotestosterone [11KT]) were monitored througho ut the spawning season. Female sole sampled July through early Septemb er were primarily regressed or previtellogenic and had low GSI and pla sma steroid levels. GSI and plasma steroid levels were also low in mal e sole sampled during this time, but the majority had already entered spermatogenesis and, in some fish, production of mature sperm was obse rved. Fish sampled in October were in the early stages of vitellogenes is and spermiogenesis and showed increases in GSI and plasma steroid l evels. By November, about 50% of female fish had entered vitellogenesi s and about 30% of males were producing sperm. Proportions of vitellog enic females and sperm-producing males continued to increase through J anuary, with significant numbers of spawning females and males present in February. By late March, the majority of both sexes were spent. Vi tellogenic female sole had the highest plasma E2 levels, vitellogenic sole with hydrated oocytes had the highest GSI, and spawning female so le had the highest plasma T levels. Plasma T, 11KT, and GSI were highe st in spawning male sole. Reproductive parameters returned to baseline levels in spawned out female and male sole. A potent maturation-induc ing steroid (MIS) in many species of teleosts, 17 alpha,20 beta-dihydr oxy-4-pregnen-3-one, was not detected in spawning English sole. Additi onal research is needed to identify the MIS in English sole and to und erstand better the hormonal regulation of early gonadal development in male sole.