Gonadal development and plasma steroid levels during pubertal development in captive-reared striped bass, Morone saxatilis

Puberty is the period during which full sexual development occurs and the c apacity to reproduce is acquired. Despite its importance, our understanding of the endocrine regulation of puberty in lower vertebrates is still limit ed. The objective of the present study was to describe the changes in gonad al development and plasma steroid levels in a relatively late maturing spec ies,the striped bass, during the first four years of life. In about 65% of the females, puberty was initiated during the third year. Although gonadoso matic index (GSI) and oocyte diameter increased during this year, this firs t cycle was characterized by a heterogeneous population of developing oocyt es, a relatively low mean maximum oocyte diameter, and an absence of yolk g ranules in the oocytes. Plasma 17 beta-estradiol (E-2) levels were low in a ll three-year-old fish, suggesting that an insufficient stimulation of vite llogenin production by E-2 may underlie the lack of vitellogenin incorporat ion into developing oocytes. All monitored parameters increased during the fourth year, but were still below the values attained by older females. In about 60% of the males, puberty was initiated during the first year and all males were mature by the third year. During the first two years, several i mmature males initiated spermatogenesis without reaching full maturity. In mature males, mean GSI, plasma testosterone, and 11-ketotestosterone levels increased simultaneously, reaching higher values each subsequent year. Our results indicate that, similar to the situation in mammals, more than one reproductive cycle is required in striped bass before complete adulthood is reached. J. Exp. Zool. 286:49-63, 2000. (C) 2000 Wiley-Liss, Inc..