Induced maturation and fertilized egg production of the red‐spotted grouper, Epinephelus akaara , using adaptive physiology of photoperiod and water temperature

Abstract

As a preliminary investigation into the effects of environmental factors on gonadal development using adaptive physiological characteristics, we examined the involvement of photoperiod and water temperature in the ovarian development of the red‐spotted grouper, Epinephelus akaara. During October 2014 (non‐breeding season), the photoperiod and water temperature were adjusted to 12L:12D and 18°C respectively. Every 3 weeks, daylight was increased as follows a 13L:11D and 14L:10D in the photo‐thermal treatment group, and the control group was maintained under natural conditions. After 9 weeks, water temperature was increased to 23°C in the photo‐thermal treatment group. In photo‐thermal treatment group, GSI increased significantly after 9 weeks (1.36 ± 0.19) and 12 weeks (3.31 ± 0.20) compared with the control group. At 12 weeks after photo‐thermal treatment, all fishes matured into ovaries containing late vitellogenic oocytes. The expression of FSHβ and LHβ mRNAs also increased significantly. However, in the control group, the ovarian development was maintained at an immature stage. Based on these results, we demonstrate that exposure to long photoperiod and high water temperature can induce the sexual maturation of immature red‐spotted grouper during the non‐breeding season.

Response of body color change rearing under different light intensity conditions in farmed red spotted grouper, Epinephelus akaara

“…These countries contribute 92% of the total production of grouper (Rimmer and Glamuzina 2019). Numerous grouper species studies have been performed on larval development stages as well as the growth and reproductive characteristics (Chauvet 1988;Song et al 2005;Kim et al 2013;Lee et al 2014;Lee et al 2020).…”

“…Serranidae have high industrial value in the domestic aquaculture industry, and some studies (growth (Cho et al 2015), maturity (Lee et al 2020), development (Song et al 2005), digestive physiology (Hur et al 2013), etc.) are being performed for the development of aquaculture technology.…”

Mature and Bi-Sexual Phase Gonad Occurrence in Cultured Red Spotted Grouper, Epinephelus akaara

“…E. akaara juvenile growth is slower than other Korean-cultured grouper species (e.g., Epinephelus bruneus and Hyporthodus septemfasciatus ) ( Lee & Hur, 1998 ; Song et al, 2008 ). The low growth rates have prompted most red spotted grouper studies to focus on inducing growth, puberty, maturation, and sex inversion via changes in the water temperature, varied photoperiods, and exogenous hormone treatments ( Li et al, 2005 ; Li et al, 2006 ; Lee et al, 2014 ; Cho et al, 2015 ; Lee & Baek, 2018 ; Oh et al, 2018 ; Lee et al, 2020 ). These studies showed that if red spotted grouper juveniles (110 days after hatching) were reared for eight months in a natural photoperiod and warm water, then the GSI increased as the water temperature increased ( Oh et al, 2018 ).…”

“…The red spotted grouper, Epinephelus akaara inhabits Korea, southern China, Taiwan, and Japan ( Lee et al, 2020 ). Originally reported as protogynous hermaphrodites ( Tseng & Ho, 1988 ; Zhang et al, 1988 ), studies now show they are bidirectional sex changers in laboratory conditions ( Okumura, 2001 ; Chan & Sadovy, 2002 ; Liu & Sadovy, 2004 a , b ; Liu et al., 2016 ), and sexual-pattern plasticity between wild and reared fish has been proposed ( Liu et al, 2016 ).…”

“…Several studies have been conducted to investigate red spotted grouper reproduction in laboratory conditions for commercial seed production ( Li et al, 2005 , 2006 ; Lee et al, 2014 ; Oh et al, 2018 ; Jeon et al, 2020 ; Lee et al., 2020 ), and there is increasing interest from Korean fish farms for commercial cultivation. In this study, we report the occurrence of mature and bi-sexual phase gonads in red spotted groupers reared for less than a year.…”