Using estradiol and progesterone concentrations to assess individual variability in the reproductive cyclicity of captive female little skates, Leucoraja erinacea, from the western Gulf of Maine

Abstract

In the current study, plasma steroid hormones were used to assess the individual variability of Leucoraja erinacea over the course of 12 months, in hopes of further defining its reproductive cycle. No statistical differences in hormone concentrations were observed between the isolated and non-isolated female skates. Monthly E2 concentrations ranged from 1,430 pg ml(-1) in August to 3,940 pg ml(-1) in March, indicating the presence of mature ovarian follicles and supporting the conclusions from previous studies that L. erinacea is capable of reproducing year-round. Concentrations of E2 were significantly elevated or depressed during some months (February, March, June, July, August, and September) of the year, suggesting that reproductive activity may vary over the annual cycle. Even though monthly P4 concentrations were highly variable, ranging from 82 pg ml(-1) in November to 816 pg ml(-1) in September, no significant reproductive peaks were observed. In addition, a persistently large variation in E2 and P4 concentrations, indicative of reproductive asynchrony within (mean CV 62% and CV 69%, respectively) and between (mean range CV 78 and 125%, respectively) individual skates, was observed throughout the study. Collectively, the continually high E2 concentrations and variability in both hormones observed in the current study are indicative of an oviparous species that reproduces actively throughout the year. However, the weekly sampling frequency revealed that plasma E2 concentrations, not P4, were more useful to assess reproductive status in asynchronous continuously breeding oviparous elasmobranchs.