Studies on embryonic and larval development of sea cucumber (Holothuria scabra)

At present,the cultivation of sea cucumber in China is mainly concentrated in the north.The main rearing species is Apostichopus japonicu.However,in the southern part of China,the high temperature of water is not fit for the cultivation of A.japonicu.As a result,to meet market demand,developing the cultivation of tropical sea cucumber is very necessary.Holothuria scabra is one of common tropical sea cucumbers with high economic value in Hainan.In this thesis,to enhance the seeding technology of H.scabra,the embryonic and larval development of H.scabra was observed and recorded.The heights of fertilized eggs,embryos and larvae were measured under the light microscope,and the time series table of embryonic and larval development was confirmed.The results show that the bloodstocks were spawned artificially by using the method of streaming and drying in the shade jointly.A large number of fertilized eggs were gathered and the fertilized rate was over 90%.The embryonic and larval development of H.scabra can be divided into the following stages: fertilized egg,cleavage,blastula,rotary blastula,gastrula,early auricularia,mid auricularia,late auricularia,doliolaria,pentactula and juvenile.At the average temperature of 29 ℃ and salinity of 34,the fertilized eggs needed 3 hours to develop to the blastula,and 4 hours to the rotary blastula,5 hours to the gastrula,and 19 hours to auricularia.Then it took about 7 days to develop to the doliolaria and 15 days to develop to juvenile sea cucumber.Through the observation,the conclusion can be drawn that the polyspermy can make the embryo become developmental abnormal.In the end,the development ceased and the creature died.The sizes of larval arms and the appearance of globoid at the big auricularia stage can be used as the important indexes for evaluating the healthy status of the larva of H.scabra.The bigger the larval arms,the higher the appearance rates of globoid were,the higher the metamorphic rates and survival rates of the larva were.Through the comparison with larvae of other kinds of sea cucumbers,the conclusions are obtained that there is a salient structure at the end of larval body of H.scabra,but A.japonicus and Australostichopus mollis have no such organ;while the difference gives rise to the result that the sites of ossicles of different kinds of sea cucumbers are not the same.And,the schedules of the embryonic and larval development are different from H.scabra to other species of sea cucumber.The research could provide dependable data,photos,measures of disease control for the H.scabra larva cultured production to contribute to the exploitation and development of aquaculture of southern sea cucumber.So the market demand could be met and the natural resources could be protected.