Alterations in serum steroid concentrations in the clearnose skate, Raja eglanteria: Correlations with season and reproductive status

Serum steroid hormones in the peripheral circulation of the clearnose skate, Raja eglanteria, were measured at the time of capture and at various times throughout the year while the animals were maintained as a captive breeding population. These analyses demonstrate interesting correlations between changes in hormone concentrations and annual reproductive events. Animals were sampled once (78 females, 20 males) or multiple times (15 females). For both groups of females, 17β-estradiol was detected throughout the year with significant elevations occurring during October and November when ovarian follicles begin to mature (as determined through necropsy examinations), and January and February when maximum mating activity is observed and egg laying begins. Testosterone and dihydrotestosterone concentrations were significantly elevated in females only during January and February. Testosterone elevations were synchronous with longer-term elevations in 17β-estradiol in females sampled either once or repetitively. Testosterone concentrations in males were significantly elevated during times of maximum breeding activity compared to periods of sexual inactivity. Data from females sampled during five stages of the egg laying process, as defined by the position of palpable egg capsules within the reproductive tract, revealed that 17β-estradiol was highest when egg capsules were forming in the nidamental gland (stage 2) or uterus (stage 3), testosterone and dihydrotestosterone were maximal when eggs were in the uterus (stage 3) or cloaca (stage 4); and progesterone was significantly elevated immediately after oviposition (stage 5), suggesting a possible role for progesterone in the regulation of sequential laying of egg pairs.