Research Article
Sueng-Bo Oh, Chi- Hoon Lee
Abstract
It takes quite a long time for the grouper to spawn. In the case of red spotted grouper (Epinephelus akaara), at least three to four years of rearing is usually required to reproduce them for the first time. Reproductive control techniques can be applied to repress, delay or advance the onset of puberty. Thus, they can be used to accelerate the process of selective breeding in this species. The present study investigated whether alterations of rearing water temperature (WT) can advance the onset of puberty in the red spotted grouper. Juvenile red spotted grouper (110 DAH, 7.25 ± 0.5 cm, 6.45 ± 1.5 g) were randomly divided into 4 groups and reared for approximately 10 months (from Nov. 2014 to Aug. 2015) at four different WT: natural condition (12.6-19.5°C), 20 ± 0.5°C, 24 ± 0.5°C and 28 ± 0.5°C treatment. When they were reared at 24 ± 0.5°C or 28 ± 0.5°C WT, sexually mature individuals appeared within 12 months after hatching during their breeding season (Jul. to Aug.). The mRNA levels of reproduction-related genes such as Kisspeptin, GnRH, FSHβ and LHβ were higher in the 24 ± 0.5°C and 28 ± 0.5°C treatment group than the other groups (P< 0.05). Mature yolk stage oocytes (≥300 μm diameter) were found in the ovaries of female red spotted grouper reared at 24 ± 0.5°C or 28 ± 0.5°C groups, while only oogonia were found at natural condition and peri-nucleolus stage oocytes were observed at 20 ± 0.5°C group, respectively. The one-year-old mature females ovulated 6-10 ml of eggs that corresponded to 10% of their body weight. In artificial fertilization performed at 24 ± 0.5°C WT, the fertilization and hatching rates were determined to be 95% and 97%, respectively. This is the first report demonstrating that rearing at 24 or 28℃ WT can significantly advance the onset of puberty in the red spotted grouper.