Histological observations of seasonal reproductive and lunar-related spawning cycles in the female honeycomb grouper Epinephelus merra in Okinawan waters

Seasonal reproductive and lunar-related spawning cycles of the female honeycomb grouper Epinephelus merra inhabiting Okinawan waters were examined by histological observation of ovaries. Gonadosomatic index (GSI) increased beginning in May and peaked in June. Histological observations revealed that many oocytes laden with yolk were present in the ovaries from May to August. From September to October, ovaries were occupied by immature oocytes. These results suggest that the reproductive season of E.   merra lasts for 4 months from May through August in Okinawan waters. When the fish were collected according to the lunar cycle, GSI increased with the approach of the full moon. Oocytes at various development stages were observed from the first quarter to the full moon. Fresh ovulatory follicles were present in the ovaries around the last quarter moon. These results suggest that E.   merra has a lunar spawning cycle and spawns between the full moon and the last quarter moon. Ovarian features of the fish collected around the last quarter moon were different among individuals; some fish had many oocytes at the tertiary yolk stage in the ovaries, while the ovaries of the others were occupied by the oocytes at the peri-nucleolus and the oil droplet stages. This observation suggests that a minor release of eggs occurs in this species before or after a major spawning lunar day. Oocytes at the migratory nucleus and the maturation stages were not observed in any ovarian samples. This may mean that maturation of oocytes is related to the spawning behavior of this species and makes rapid progress in the process of aggregation at the spawning sites.     

HCG与LHRHa对雌性蜂巢石斑鱼产卵期间生理变化的影响及比较

选取日本冲绳地区雌性蜂巢石斑鱼为对象,描述与分析了HCG与LHRHa对该鱼催产效果的差异及注射后所引起的性腺发育变化和排卵相关的性类固醇变化,希望能为蜂巢石斑鱼的人工繁殖提供可靠的理论基础,以及在实践生产中的重要参考。结果表明,HCG与LHRHa均显著促进了决定排卵的性成熟诱导物质MIS的释放以及鱼的产卵; 产卵后的蜂巢石斑鱼雌二酮E2的水平显著下降,验证了蜂巢石斑鱼卵巢发育及产卵随月亮周期变化的周期性; 在渔业生产中注射催产药物前,确定对象鱼卵泡发育阶段对于提高催产成功率十分重要。在LHRHa注射组,完成卵黄化的蜂巢石斑鱼催产效果最佳,卵黄化早期的鱼不产卵; HCG对卵泡发育初期的蜂巢石斑鱼的催产效果优于LHRHa,但催产效果仍不理想,而对于完成了卵黄化鱼的催产效果不如LHRHa。结合LHRHa的其他优势,本研究认为在具备检验鱼体卵巢发育阶段实验技术的条件下,更加推荐LHRHa作为雌性蜂巢石斑鱼的催产药物。     

4种石斑鱼亲缘关系的RAPD分析

采用9个引物,对湛江沿海野生蜂巢石斑鱼、鲑点石斑鱼、点带石斑鱼及黑边石斑鱼的基因组DNA进行了RAPD分析,研究结果表明:蜂巢石斑鱼、鲑点石斑鱼、点带石斑鱼及黑边石斑鱼种间遗传距离(Dij)分别为0 4009(蜂巢石斑鱼-鲑点石斑鱼)、0 4805(蜂巢石斑鱼-点带石斑鱼)、0 5703(蜂巢石斑鱼-黑边石斑鱼)、0 4409(鲑点石斑鱼-点带石斑鱼)、0 4561(鲑点石斑鱼-黑边石斑鱼)及0 4729(点带石斑鱼-黑边石斑鱼);用UPGMA法对这4种石斑鱼进行聚类分析可知,蜂巢石斑鱼与鲑点石斑鱼首先聚在一起(0 4009),而后蜂巢石斑鱼-鲑点石斑鱼与点带石斑鱼聚在一起(0 4611),最后,蜂巢石斑鱼-鲑点石斑鱼-点带石斑鱼再与黑边石斑鱼聚在一起(0 4951)。在所研究的类群中,蜂巢石斑鱼和鲑点石斑鱼有较近的亲缘关系。     

Embryonic and larval development of honeycomb grouper Epinephelus merra Bloch

Spawning and successful rearing of larvae of honeycomb grouper Epinephelus merra Bloch 1793 upto juvenile stage was accomplished at the finfish hatchery of Mandapam Regional Centre of Central Marine Fisheries Research Institute during 2004. The fertilized eggs were free, spherical and buoyant with size ranging from 710 to 730 μm. Complete early embryonic development took place within 24–27 h and hatching occurred. The hatchlings measured 1.5 mm. Mouth opening (115 μm) appeared at 72 h when the larvae were 2.2 mm in size. Pectoral fin developed on the fifth day. Complete metamorphosis took place and by the 60th day the larvae transformed into juveniles (45 mm) and attained skin colouration and honeycomb pattern.