Plasma Estradiol, Testosterone, and Progesterone Levels during the Ovulatory Cycle of the Skate (Raja Erinacea)1

Abstract

Amounts of estradiol, testosterone, and progesterone in plasma were measured during the reproductive cycle of female Raja erinacea. Estradiol titers correlated directly with follicle size in females undergoing ovarian recrudescence, while highest concentrations were found in females with preovulatory follicles. These data indicate that as follicles grow, their steroidogenic capacity increases. In mature, nonspawning females, titers of estradiol and testosterone varied markedly. Progesterone was not detected in peripheral plasma of skates that did not produce eggs during the observation period. In females producing eggs, estradiol and testosterone predominated during the follicular phase of each spawning cycle. While estradiol and testosterone were elevated, progesterone was not detectable in the peripheral circulation. As ovulation and formation of capsules approached, plasma estradiol and testosterone declined to near baseline levels. Circulating progesterone rose sharply two days before encapsulation of ovulated eggs and remained elevated for only two days. On the day of encapsulation, concentrations of plasma progesterone had fallen to nearly baseline levels. Progesterone titers remained low throughout egg retention and oviposition. These measurements demonstrate that progesterone titers are elevated at specific times during the reproductive cycle of the skate and clearly suggest that progesterone is critically involved in events occurring at ovulation, encapsulation, and possibly oviposition.

Non-lethal assessment of reproductive characteristics for management and conservation of sharks

“…Over the last decade there has been an increased understanding of the reproductive endocrinology of chondrichthyans (Koob et al 1986, Koob & Callard 1999, Gelsleichter 2004, Sulikowski et al 2005. Only a few studies have compared the levels of plasma steroid hormones between juvenile and adult chondrichthyans, and all of these suggest that hormones could be used as an indicator of maturational status (Rasmussen & Gruber 1990, 1993, Rasmussen & Murru 1992, Gelsleichter et al 2002.…”

Seasonal and life-stage variation in the reproductive ecology of a marine apex predator, the tiger shark Galeocerdo cuvier, at a protected female-dominated site

“…A significant difference in the observance of both non-gravid and gravid mature females by month was observed, with a higher frequency of mature non-gravid females in May, October and November, and a higher frequency of mature gravid females in October and December these hormones are associated with follicular growth leading to ovulation (Koob & Callard 1999, Awruch 2013. Although the role that testosterone plays in viviparous elasmobranchs remains unclear (Awruch 2013), previous research suggests that this hormone is a substrate for estradiol biosynthesis (Tsang & Callard 1982) and is correlated with follicular development (Koob et al 1986). Given this, our findings suggest that the collective estradiol and testosterone concentrations can be used as a predictor of gravidity in sharks 300 cm TL and larger.…”

A comparison of reproductive parameters of the Bering skate, Bathyraja interrupta, from two Alaskan large marine ecosystems

“…Additionally, there does not appear to be any seasonal pattern to the proportion of resting B. interrupta females, as found for Alantoraja cyclophora (Oddone and Vooren 2005). Koob et al (1986) suggested that Raja erinacea, which reproduces year round, undergoes cyclic (though not necessarily synchronised) periods of reproductive inactivity and ovarian recrudescence between spawning periods. If skates have inconsistent periods of reproductive resting, this would be important to account for when quantifying lifetime fecundity for demography and fisheries management purposes.…”