An annual cycle of steroid hormone concentrations and gonad development in the winter skate, Leucoraja ocellata , from the western Gulf of Maine

Abstract

The winter skate, Leucoraja ocellata (Mitchill, 1815) is a large oviparous skate that is endemic to inshore waters of the western North Atlantic. The reproductive cycle of this species was characterized in monthly samples taken off the coast of New Hampshire, USA (42°15′N; 70°25′W), at depths of 9–107 m from November 2000 to October 2001. Plasma concentrations of the sex steroids testosterone (T), 17β-estradiol (E2), and progesterone (P4) were determined by radioimmunoassay in mature male and female skates. Changes in ovary weight, shell gland weight, and follicle size for 66 female skates were compared to patterns of all three steroid hormones. Beginning in January, ovary weight, shell gland weight, average diameter of the largest follicle, and plasma E2 increased steadily, culminating in a transient peak in July. This peak was followed by a steady decline in plasma E2 concentrations, which returned to the lowest values in December. Although T concentrations fluctuated throughout the year, a low concentration in July coincided with a peak in E2. Skates sampled in September, October, and November had the highest P4 concentrations, coinciding with the period of egg-case production. For males (n=64), annual cycles of T and E2 were compared to stages of spermatogenic development. Testosterone concentrations displayed two peaks, one in December/January and the other in July, which were associated with maximum spermatocyst concentration, while E2 peaks in February, June, and October coincided with maximum spermatocyte concentration. Along with our observations that some reproductive individuals were present throughout the year, these findings suggest that the winter skate has a partially defined reproductive cycle.