홍바리, Epinephelus fasciatus의 번식생리 특성

Abstract

Abstract

The blacktip grouper Epinephelus fasciatus are protogynous hermaphroditic fish. Female is distributed 36 to 37 cm total length and 400 to 900 g body weight. Male is distributed 34 to 41 cm total length and 600 to 1,000 g body weight. Ultrastructural characteristics of egg and spermatozoa in blacktip grouper different from those of other grouper and spermatozoal head diameter is a close correlation with egg micropylar diameter. We cloned and sequenced the cDNA encoding the follicle-stimulating hormone beta subunit (FSHβ) and luteinizing hormone beta subunit (LHβ) from the pituitary of the blacktip grouper, which regulate vitellogenesis and maturation in vertebrates. The full-length cDNAs of FSHβ and LHβ were 571 bp and 617 bp, encoding 120 amino acid (aa) and 147 aa proteins, respectively. Induction of sex maturation by environmental control investigated the involvement of photoperiod and temperature in ovarian development of the blacktip grouper. The photoperiod and water temperature was adjusted to 12L:12D and 22℃, respectively. In the treatment group, every 3 weeks daylight was increased as follows a 13L:11D and 14L:10D, and control group was maintained 12L:12D. After 9 weeks water temperature was increased 25℃ both treatment and control group. Sex maturation of blacktip grouper induced only 14L:10D and 25℃ treatment group. To development of sex maturation control rearing system of the female blacktip grouper, this study investigated the effects of photoperiod and water temperature on gonadal activity and FSHβ and LHβ mRNA expression. Photoperiod and water temperature in control group was exposed to natural conditions. Photoperiod and water temperature in treatment Ⅰ was exposed to and natural condition, respectively. In the treatment Ⅱ, photoperiod was 14L/10D and water temperature was maintained 25±0.5°C. At 12 weeks of treatment, gonad of control and treatment Ⅰ were immature stage. But, gonad of tratment Ⅱ was mature stage, and LHβ mRNA levels in pituitary on treatment Ⅱ increased significantly in comparison with initial group and the other treatment groups (P<0.05). These results suggested that the long photoperiod of 14L:10D and high water temperature of over 25℃ were essential environmental factors for the reproductive activity of the female blacktip grouper. To suitable storage and use of sperm, cryopreservation condition and survival rate and activity of thawed sperm investigated. The survival rate and activity in thawed sperm were hight using 5% and 10% glucose as the diluent and DMSO as cryoprotectants. To production of fertilized egg, hormonal induced ovulation was attempted in females with an average vitellogenic oocyte diameter of at least 400 ㎛. Induce of ovulation occurred to following HCG (500 IU/kg BW) injection. Eggs were stripped successfully 24-48h after the injection. Stripped fertilized eggs of blacktip grouper E. fasciatus were colorless spheres, 700-800 ㎛ in diameter, with a 160-170 ㎛ oil globule. Hatching began about 28h after fertilization. Yolk absorption was completed within 48h and the mouth open about 72h after hatching. In the development of larvae and juveniles, the newly hatched larvae measured 1.2 mm TL. At 2 DAH, the larvae reached 2.4 mm TL. At 12 DAH, the larvae reached 5.4 mm TL and the dorsal fin developed. At 22 DAH, the larvae reached 10.5 mm TL and began metamorphosis to post larvae stage. At 45 DAH, the larvae reached 22.4 mm TL and transferred to juvenile stage. At 60 DAH, the juvenile fish reached 30.2 mm TL and showing features with those of the adult fish. At 29 DAH, the number of gastric glands and pyloric ceca were observable. The muscular layer of the posterior stomach was increased in size and formed the pyloric sphincter, which separated the stomach from the anterior intestine. At 34 DAH, the canine-like pharyngeal tooth occurred in the buccopharyngeal cavity and the stomach size and the numbers of gastric glands continually increased. Blacktip grouper larvae developed a well-differentiated digestive system with a functional stomach at about 29 DAH. Weaning of blacktip grouper larvae to formulated feeds was started on 29 DAH at 25℃ when the functional stomach, pyloric sphincter, and pyloric ceca were formed.