Dynamics of oocyte development and related changes in serum estradiol-17β, yolk precursor, and lipid levels in the teleostean fish, Leptocottus armatus

1. 1. The dynamics of ovarian development in Leptocottus armatus were studied. Seasonal changes of serum estradiol-17β, serum vitellogenin, serum total lipids and visceral lipid reserves were monitored. 2. 2. Two to four distinct size classes (clutches) of oocytes occurred in the ovary preceding and during the spawning period. One of these clutches contained oocytes in the vitellogenic or post-vitellogenic phase, a second clutch contained oocytes “arrested” in the cortical alveoli stage and a third clutch contained non-yolky oocytes. Only one clutch was oviposited in the annual spawning season. 3. 3. Estradiol levels increased coincident with the appearance of yolky oocytes in the ovary. Serum estrogen levels were highest during the period of ovulation and spawning. During the spawning period estradiol titers were not significantly correlated with oocyte size or gonosomatic index. 4. 4. Serum vitellogenin levels increased in parallel with oocyte size and estradiol titers. Vitellogenin levels were relatively low during the early portion of the spawning period, becoming elevated again towards the end of the spawning period. In concordance with ovarian regression, serum vitellogenin levels declined and remained low during the ovarian quiescence phase. Neither GSI nor serum estradiol titers correlated significantly with vitellogenin levels. 5. 5. With initiation of ovarian recrudescence visceral lipid reserves began to decline and continued to decline through the vitellogenic and spawning phases. Visceral lipid reserves were inversely correlated with ovarian GSI. Serum lipid levels were high during ovarian recrudescence, remaining elevated through the spawning period. During the phase of ovarian quiescence serum lipid levels were low and visceral lipid reserves were high. Visceral lipid reserves showed an inverse correlation to serum estradiol titers.