REPRODUCTIVE HORMONE PATTERNS IN MALE AND FEMALE COWNOSE RAYS (RHINOPTERA BONASUS) IN AN AQUARIUM SETTING AND CORRELATION TO ULTRASONOGRAPHIC STAGING

Abstract

Reproductive management of cownose rays ( Rhinoptera bonasus) under professional care plays an important role in conservation of the species, but hormone and ultrasonographic analyses of their 12-mo reproductive cycle have not been documented previously. Plasma reproductive hormone concentrations (17B-estradiol, progesterone, testosterone, and androstenedione) were measured monthly via radioimmunoassay for 1 yr in an aquarium-managed population of adult females ( n = 15) and males ( n = 5). Ultrasounds of the uterus were performed each month at the time of sample collection to identify gestation stage (0-5) based on a previously developed in-house staging system. Stages were correlated to hormone concentrations to track progression through pregnancy. Thirteen females were reproductively active, and each produced one pup in March-June, similar to timing for free-ranging populations. Female estradiol increased steadily throughout gestation from stages 0 to 5, while progesterone, testosterone, and androstenedione were increased only in early gestation (stages 1 and 2). Unlike month of year, gestation stage strongly predicted hormone concentration, but specific values to predict parturition date were not identified. Male testosterone and progesterone were higher in March-June (mating season) than July-January, while estradiol and androstenedione did not exhibit a seasonal pattern. Aquarium-managed cownose rays have similar reproductive patterns to what is reported in wild populations. Ultrasonographic monitoring with serial hormone analysis and accurate mating records will provide the most useful information for managing a reproductive population of cownose rays in an aquarium setting.

Peer Review #3 of "Steroid hormones and chondrichthyan reproduction: physiological functions, scientific research, and implications for conservation (v0.1)"

“…Androstenedione (A4). In batoids, A4 was higher during the greater fertile period and early gestation of R. bonasus, while there were no differences in A4 along with E2 in the analysed males (Sheldon et al 2018). A similar increase was observed in early and midterm females just before the appearance of claspers in embryos of the round stingray U.…”

“…This structure becomes the egg case in oviparous species or a protective membrane in viviparous embryos (Hamlett 2011). A rise in P4, E1 and A4 occurs during the preparation for the passing of fertilized oocytes from the oviducal gland to the uterus (Di Prisco 1967;Koob et al 1986;Sulikowski et al 2004;Sheldon et al 2018). During pregnancy, this increase in P4 acts as a negative feedback for the synthesis of E2, resulting in a reduction of the vitellogenin synthesis (Tsang and Callard 1987;Tricas et al 2000;Prisco et al 2008;Mull et al 2010).…”

Steroid hormones and chondrichthyan reproduction: physiological functions, scientific research, and implications for conservation

“…In batoids, A4 was higher during the greater fertile period and early gestation of Rhinoptera bonasus, while there were no differences in A4 along with E2 in the analysed males (Sheldon et al, 2018). A similar increase was observed in early and mid-term females just before the appearance of claspers in embryos of the round stingray U. halleri, which could suggest an intermediary role for sex differentiation along with 17-OHP (Lyons & Wynne-Edwards, 2019).…”

“…A rise in P4, E1 and A4 occurs during the preparation for the passing of fertilised oocytes from the oviducal gland to the uterus (Di Prisco, Vellano & Chieffi, 1967;Koob, Tsang & Callard, 1986;Sulikowski, Tsang & Howell, 2004;Sheldon et al, 2018). During pregnancy, this increase in P4 acts as a negative feedback for the synthesis of E2, resulting in a reduction of the vitellogenin synthesis (Tsang & Callard, 1987;Tricas, Maruska & Rasmussen, 2000;Prisco et al, 2008;Mull, Lowe & Young, 2010).…”

Peer Review #2 of "Steroid hormones and chondrichthyan reproduction: physiological functions, scientific research, and implications for conservation (v0.1)"

“…Bloodstream levels of P4, S and 11KA4 favour the conditions for the maintenance of embryos, with the presence of CORT, E1 and A4 playing a role in the potential regulation of energy and stress (Fig. 6;Di Prisco 1967;Manire et al 1999;Sheldon et al 2018;Lyons and Wynne-Edwards 2019).…”