Effects of Photoperiod, Water temperature, and Exogenous Hormones on Spawning and Plasma gonadal Steroid in Starry Flounder, Platichthys stellatus

Abstract

The sexual maturation and spawning of teleosts are regulated by the external environment and the endocrine system. When the environmental conditions are artificially adjusted at a fish farm, the maturity and spawning of fish can be controlled. In this study, sexual maturation and spawning of the starry flounder, Platichthys stellatus, were artificially induced by adjusting the water temperature and photoperiod at a fish farm to accelerate the species' natural spawning period. One experimental group acted as a control and was exposed to a natural photoperiod and natural water temperature (NPNT). In contrast, another experimental group was exposed to an adjusted environment consisting of a regulated photoperiod and temperature (RPRT). Daylight time was reduced by 10 minutes every 3 days from 13 hours to a duration of 8 hours. The water temperature was first reduced by 1 o C every day, starting at 22 o C and ending at 8 o C, and then raised to 10 o C until the spawning period. Both experimental groups were treated with gonadotropin-releasing hormone analog (GnRHa) pellets to induce ovulation. The results show that when the water temperature and photoperiod were artificially controlled, ovulation could be induced 97 days earlier than the natural spawning. Plasma testosterone levels of RPRT and NPNT tended to increase and then decrease 1-2 months before spawning, and plasma levels of 17α,20β-dihydroxy-4-pregnen-3-one increased 1-2 months before spawning. The concentration of estradiol-17β (E2) in plasma was not associated with spawning. Recently, it was reported that melatonin not only plays a role in determining spawning timing in fish but also acts as an antioxidant in the control of oocyte maturation along the HPG axis (Maitra & Hasan, 2016). It is generalized that changes in the photoperiod, which regulates the reproductive cycle of fish, cause changes in maturation-related hormones and melatonin, and that maturation and spawning are regulated according to these changes (Oliveira et al., 2011).Starry flounder, Platichthys stellatus, is a fish that is widely distributed in the North Pacific Ocean from Korea, Japan, the Okhotsk Sea, and the Bering Sea to the Gulf of California (Nam et al., 2008). It belongs to the spring spawners and its spawning period is March to May in the waters of Korea (Lim et al., 2007). Recently, the demand for starry flounders has increased, and breeding companies have produced seeds using artificial insemination during the natural spawning season. However, the mortality rate of juvenile starry flounders increased when transferring the hatch to farms in summer as temperatures increased. Furthermore, female eggs do not naturally ovulate on farms for unknown reasons even though broodstocks are sufficiently matured. To solve these

Epigenetics and Probiotics Application toward the Modulation of Fish Reproductive Performance

“…In addition, photoperiod plays a significant role in accelerating maturation and spawning of Scophthalmus maximus (Turbot) [90]. Many commercially important fishes, such as O. mykiss [93], Dicentrarchus labrax (sea bass) [94], O. niloticus [95], D. rerio [96], Platichthys stellatus (starry flounder) [97], and C. magur [98], respond to the changes of photoperiod, leading to the onset and completion of gonadal maturation and spawning.…”

Photoperiod manipulation leads to successful voluntary captive spawning of butter catfish Ompok bimaculatus during the non‐spawning breeding season

“…GtH stimulates the gonads and promotes the secretion of sex steroid hormones. Thus, plasma levels of sex steroid hormones provide essential information regarding the fish's reproductive cycle and maturation (Hong et al, 2021).…”

“…GtH stimulates the gonads and promotes the secretion of sex steroid hormones. Thus, plasma levels of sex steroid hormones provide essential information regarding the fish's reproductive cycle and maturation (Hong et al, 2021). It is generalized that changes in the photoperiod, which regulate the reproductive cycle of fish, cause changes in maturation‐related hormones (Oliveira et al, 2011).…”