The Research On Biological Characteristics And Pearl Performance Of Hyriopsis Schlegelii

Hyriopsis schlegelii which was original distributed in Japan is the famous freshwater clam,it is various species of the genus Hyriopsis cumingii which was original distributed in China.It was introduced into China by Nancheng Reservoir Exploitation Company in Fuzhou in 1997.In this research,we focus on the biological characteristics,propagation and artificial breeding techniques and pearl performance characteristics.In order to provide some theoretical and practice instructions of freshwater pearl cultivation in our country,to work out the problem of unitary species of pearl clam,to promote a healthy and sustainable development of freshwater pearl cultivation.First,the biological characters were investigated.The external and internal morphology of H.schlegelii are almost as same as H.cumingii wit regional variations.The countable and measurable properties data indicated that shell width of H.schlegeli is as1.23 times as H.cumingii.Paraffin section and SEM(Scanning Electron Microscope) observations showed the crystalline style of H.schlegeli is longer and larger diameter than H.cumingii,the mantle depth of H.schlegeli is as1.78 times as H.cumingii,and the nacre shell is 2.08 times.The basic unit of structure of nacre is aragonite tablet,which become more and more thickly as the growth of H.Cumingii.The average growth speed of H.schlegeli is faster than H.cumingii,which were the same sizes,culture density and cultured in the same water.Second,the propagation and artificial breeding techniques of H.schlegeli was carried out.The results demonstrated that 3 years old H.schlegeli are partial maturation and 4 years old clam are the best ones,they also keep this capability till 6 winter ages.The season of propagation is from May to July,can ovulate many times,and the ovum matured at different times,one matured female clam can ovulate 4～5 times per year.The results showed that the glochidia of H.schlegeli were hooked.The optimum temperature range of the embryonic development was 24～36℃,the hatching time of the embryonic development more shorter when the temperature is higher than 30℃,the accumulated temperature of the embryonic development was 247.2℃.In the host fish,the number of glochidia was varied in the part of body,number of branchias was most,and diposefins was least,the average number of parasitic is 1985 per fish.The average fecundity of selective F₃ generation was 13.9 thousands per one,and the survival rate of larvae was 82.6%.The survival rate of preparation clam for nucleated pearl producing and all-nacre pearl producing were 86%and 82.3%,and the compliance rates for operating were 78% and 95%.Third,pearl performance was carried out on H.schlegeli and H.cumingii,including nucleated pearl producing and all-nacre pearl producing.The results indicated H. schlegeli has significantly high advantage in pearl performance than H.cumingii.The survival rate of operative mussel of H.schlegeli was higher than H.cumingii both of nucleated pearl producing and all-nacre pearl producing.The thickness of pearl layer and the quality of pearl in nucleated pearl,the yield of all-nacre pearl were also better than H.cumingii,especially in three kinds of best all-nacre pearl,which the diameter are 8mm, 9mm and more than 10mm.At the same time,the pearl performance of F₃ generation was better than F₂ generation,it indicated the advantage of selective improved variety.The results indicated that H.schlegeli has best morphology for culturing pearl,the propagation and artificial breeding techniques were matured,the pearl performance was better H.cumingii.It can be widly use in freshwater pearl cultivation in our country.