Long-term monitoring of egg-laying cycle using ultrasonography reveals the reproductive dynamics of circulating sex steroids in an oviparous catshark, Scyliorhinus torazame

• Published in: General and comparative endocrinology Vol. 327; p. 114076
• Main Authors: Inoue, Takuto, Shimoyama, Koya, Saito, Momoko, Wong, Marty Kwok-Shing, Ikeba, Kiriko, Nozu, Ryo, Matsumoto, Rui, Murakumo, Kiyomi, Sato, Keiichi, Tokunaga, Kotaro, Kofuji, Kazuya, Takagi, Wataru, Hyodo, Susumu
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.10.2022
• Subjects: Cloudy catshark; Egg-case formation; Egg-laying cycle; Progesterone; Ultrasonography; Cloudy catshark; Progesterone; Egg-laying cycle; Egg-case formation; Ultrasonography
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1016/j.ygcen.2022.114076

•Long-term monitoring of catsharks was conducted using portable ultrasound device.•This approach succeeded to detect continuing egg-laying cycles non-invasively.•Simultaneous measurement revealed cycling pattern of plasma sex steroids.•A progesterone surge occurs just before ovulation/egg-case formation.•Catshark serves as an excellent model in elasmobranch reproductive endocrinology. The many diverse reproductive strategies of elasmobranchs (sharks, skates and rays) from lecithotrophic oviparity to matrotrophic viviparity have attracted significant research attention. However, the endocrine control of elasmobranch reproduction is less well-documented largely due to their reproductive characteristics, such as a long reproductive cycle, and/or repeated internal fertilization using stored sperm in oviparous species. In the present study, for the first time, we succeeded in non-invasive monitoring of the continuing egg-laying cycle of the cloudy catshark Scyliorhinus torazame using portable ultrasound devices. Furthermore, long-term simultaneous monitoring of the egg-laying cycle and measurement of plasma sex steroids revealed cycling patterns of estradiol-17β (E2), testosterone (T) and progesterone (P4). In particular, a decline in T followed by a reciprocal surge in plasma P4 were consistently observed prior to the appearance of the capsulated eggs, implying that P4 is likely associated with the ovulation and/or egg-case formation. While the cycling pattern of E2 was not as apparent as those of T and P4, threshold levels of E2 (>5 ng/mL) and T (>1 ng/mL) appeared to be crucial in the continuation of egg-laying cycle. The possibility to trace the dynamics of plasma sex steroids in a single individual throughout the reproductive cycles makes the catshark a useful model for regulatory and mechanistic studies of elasmobranch reproduction.