Studies On The Artificial Induction Of Polyploidy And Its Effect On Growth And Development Of Triploid In Half-Smooth Tongue Sole (Cynoglossus Semilaevis)

Half-smooth tongue sole (Cynoglossus semilaevis) is a kind of special rareeconomic cultured marine fish species in the northern China, and mainly distributed inthe north China coast. It has been the most important fish species in the northern China.But, half-smooth tongue sole exhibits sexually dimorphic growth, with females growingthree to four times faster than males. The low growth rate of males weakens the qualityof the fish, and leads to an overall reduction in production. A solution to this problemmay be found in the production of polyploidy fish.Many studies have reported that polyploidy fish especially triploid fish show bettergrowth and reproductive performance than normal diploid fish, which are benefit forfish breeding and traits improvement. In order to improve the breeding benefit andaccelerate the growth rate of half-smooth tongue sole, pressure shock are used to inducetriploidy and tetraploidy in half-smooth tongue sole. The main research results aresummarized as follows:The development of all-triploid stocks would be significantly benefit commercialaquaculture of half-smooth tongue sole. In order to stably attain the all-triploid stocks, aset of experiments were carried out for developing induce tetraploid technique inhalf-smooth tongue sole. The optimal initiation time for pressure shock of fertilizedeggs was determined to be21.5min after fertilization when the water temperature is23±0.2℃. The optimal pressure and treatment duration were determined to be40MPaand4.5min, and the tetraploid rate of fry was68.3%. Ploidy of fry was analyzed usingPloidy analyzer, which proved that the tetraploid DNA relative content was two timesthan the normal diploid fry.84chromosomes were observed in artificial triploid fry,while the normal diploid fry has42chromosomes. Thus, a protocol for the induction of tetraploid fry was developed for the first time in half-smooth tongue sole in the presentstudy, which lays the foundation for production of all-triploid stocks in half-smoothtongue sole.In the present study, a set of experiments were carried out for developing artificialall-triploids technique in the tongue sole. First of all, the optimal initiation time forpressure shock of fertilized eggs was determined to be5min after fertilization when thefertilized eggs were incubated at water temperature of about23±0.2℃, the optimalpressure and treatment duration were determined to be36MPa and4min, respectively.Ploidy of fry was analyzed using Ploidy analyzer. Under the optimal inductionconditions,100%triploids were obtained.63chromosomes were observed in artificialtriploid fry and,42chromosomes were observed in normal diploid fry. Thus, a set oftechniques for induction of triploid fry was developed for the first time in half smoothtongue sole, and100%triploid fry were obtained.The gonadal development, sex ratio and growth of triploid half-smooth tongue solewere studied in this paper. The gonadal development of triploid half-smooth sole wasstudied through the anatomical and histological observation, and the result showed thatthe triploids had undeveloped gonads and were sterile. Sex identification of triploidhalf-smooth sole showed that the rate of female triploid fish was just11%, whichsignificantly lower than the diploid group. The triploid growth rates (body full-length,weight) were not significantly different compared to the diploid controls before240days. These findings can be the data support of theoretical basis for the polyploidybreeding in half-smooth tongue sole.