Conditioning, maturation and year-round natural spawning of orange-spotted grouper, Epinephelus coioides (Hamilton, 1822), in recirculating aquaculture system

摘要

The present experiment was aimed at studying the conditioning, maturation and natural spawning of orange-spotted grouper, Epinephelus coioides, in a recirculatory aquaculture system (RAS). Thirty fish (n=30; 3.35 +/- 0.05kg) were stocked in a circular tank of 125m(3) capacity fitted with an RAS for conditioning and broodstock development. After 15days, 15 fish were implanted with 17 methyl testosterone and letrozole at the rate of 5mg and 0.2mg/kg body weight, respectively, for conversion from female to male. The gonadal development started after 1month, and by 90th day, 63.53 +/- 3.78% and 2.07 +/- 0.84% of the oocytes attained a size of 400-500m and 500-600m respectively. Natural spawning commenced in the RAS from 4th month onward after stocking and spawning continued round the year. The spawning pair showed courtship behaviour with a typical vertical burst of swimming just before release of gametes. The total number of eggs spawned during 1year was 47.23 million with spawning frequency varying form 5 to 13 times per month. The association of spawning events with new moon day (lunar cycle) weakened as time progressed. The mean monthly fertilization and hatching rates varied from 77.80 +/- 3.34% to 83.70 +/- 1.76% and 82.80 +/- 4.21% to 88.33 +/- 1.39% respectively. The study proved that RAS is an efficient system that provides a stable, controllable and conducive environment for year-round natural breeding of orange-spotted grouper.