Induction of Puberty in Red Spotted Grouper, Epinephelus akaara By Water Temperature

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.

Effects of Various LED Light Spectra on Growth, Gonadal Development, and Growth-/Reproduction-Related Hormones in the Juvenile Red Spotted Grouper, Epinephelus akaara

“…However, in the second month, from 24 August to 23 September, the average water temperature was only 23.4 °C. In previous studies, it was shown that higher water temperatures could induce faster growth of channel catfish, Ictalurus punctatus [ 39 ], largemouth bass, Micropterus salmoides [ 40 ], and red spotted grouper [ 41 ]. In this study, it was possibly the higher water temperature and white LED that caused the red spotted grouper to achieve a significantly higher CF in the first month.…”

“…However, there were no significant differences in FSHβ and LHβ expression among the four light groups. Recently, the endocrine system of the Kiss-GnRH-GtHs axis was considered a potent regulator of reproduction in grass puffer [ 48 ], European sea bass [ 49 , 50 ], striped bass, Morone saxatilis [ 51 ], and red spotted grouper [ 41 ]. Until now, FSHβ has been widely known to be active as a key hormone in mediating early vitellogenesis and spermatogenesis, whereas LHβ is generally associated with final maturation and ovulation or spermiation in the salmonid fish [ 52 , 53 , 54 ], Japanese conger, Conger myriaster [ 55 ], Japanese eel, Anguilla japonica [ 56 ], and European sea bass [ 57 ].…”