Reproductive biology of scatophagus argus and artificial induction of spawning

Scatophagus argus is a highly commercially valuable fish,which is strongly resistant to environmental stress.In this study,the authors focus on the reproductive biological feature and general growth activity of cultured Scatophagus argus using experiments of artificial induction of spawning.The results indicate that the sex ratio of male to female Scatophagus argus is 1:1.31.The minimum biological age of reproduction is 1 for both female and male.Two-year-old parent fish adapts quickly to artificial breeding.The period from April to August is the reproductive season for Scatophagus argus in South China coastal waters.The peak of spawning season is between May and July.The absolute fecundity of individual female is 337309 to 635755 in number,with an average of 456320.The relative fecundity of individual is 720.4 to 963.3 per gram in number and 843.1 on average.Scatophagus argus is dioecious.The GSI(gonadosomatic index) of female fish is up to 14.74% while that of male is up to 2.2%.It is necessary for this fish to spawn in water of higher salinity.The fish is capable of multiple spawning during its reproductive period.Under appropriate circumstances,sexually mature female fish is able to spawn by the induction of mixed hormone [15μg·kg-1 LHRH-A2(Luteinzing Hormone Releasing Hormone-analogue) +3.0-4.0mg·kg-1 DOM(Domperidone) or 15μg·kg-1 LHRH-A2 +1000-1500Iu·kg-1HCG(Human Chorionic Gonadotropin)] and fertilize natu-rally in captivity.The phases of the moon and the tides do not influence the induction of Scatophagus argus spawning apparently.Scatophagus argus spawns pelagic eggs with single oil globules.The diameter of its eggs is about 750 μm.The number of its oosperms per gram is about 3500 to 3800.The development of embryos takes 20-24 h to hatch larvae at the water temperature of 27-29℃ and salinity 25‰.The length of newly hatched larvae is 1.75 to 1.88 mm.The length of four-day-old larvae,yolk sacs of which have disappeared,is 2.6 to 2.8 mm.Then the baby fish starts to feed on plankton larvae,and soon turns into nutritional transition period.