The Study On Reproduction And Embryogenesis Of Procambarus Clarkii

The red swamp crayfish Procambarus clarkii(Cirard)belongs to Decapoda, Reptantia,Cambaridae,Procambarus.It originally distributed in the north of Mexico and the south of America,and was introduced into China by Japanese in the 1930s.Now it distributes in more than 10 provinces of China.It has adverse effect to the plants,pools,dams because of its troglodytism,it has been treated as an pest for many years.But recently,with the improvement of people's living standards,this swamp has become more and more popule because of its delicious taste and abundant nutrition.Now it has become one of the most important freshwater aquatic products in the cultivation. However,the natural resource of this crawfish has been decreased dramatically in recent several years because of its economic value and fishing without limit.Meanwhile,thers is no successful experiment or technology to support the artificial cultivation,leading this conomical aquatic animals could not meet the need of the consumption.So the artificial reproduction technique is imminently required to be developed for protecting the resource and for meet the need of the markets.In this study,we have investigated the reproductive biology and the changes of main digestive enzymes during embryonic development of the Procambarus clarkii Giard.The data may provide a base for developing the artificial reproductive technique.1.Investigation on the reproductive period of Procambarus clarkii.In order to provide the basic documents for developing the technique of artificial reproduction of this crayfish,the reproductive period of P.clarkii in Wuhan area was investigated by paraffin section in this paper.The asynchronism of oogenesis was observed in the sections of ovaries.The mature eggs appeared in the sections of the ovaries sampled in two periods.One period was from April to May,the other one was from September to October.The large eggs contained abundant yolk granules.In June to July and November, more previtellogenic and initial vitellogenic oocytes were observed in the ovaries,while there were a few eggs in degeneration,indicating that those periods might be after spawning and starting a new round of oogenesis.In testis of the crayfish,the proportion of the testicular tubules containing the spermatids and sperm increased dramatically in both periods of April to June and September to October,although there also appeared the spermatocytes during these two periods.Furthermore sperms contained in the vas deferens were frequently observed in these two periods.While the ratio of the testicular tubules containing spermatogonia and spermatocytes were higher in other periods during a year.These results suggest that in one year there are two periods of reproductive peak of P.clarkii in Wuhan area which are from April to May and from September to October, respectively.2.Investigation on the embryonic development of Procambarus clarkii.The results show that the colour of the eggs change garadually during the egg development:gray with yellow—gray—gray with brown—brown—tan—total black.The process of embryonic development could be divided into seven stages:fertilized eggs stage, cleavage stage,blastula stage,gastrula stage,egg-nauplius,embryo with compound eye pigments forming,prehatching stage.There were no significant difference in egg size at the early stages.However,the egg size increased about 0.78mm near the prehatching stage.Embryogenesis of this crawfish normally lasts 25-33 days at the water temperature of around 25℃.The whole eggs were around by protective coating in the early period of embryonic development,but the larval was similar to the adult from the morphology while it had just hatched.3.Investigation on the changes in main digestive enzymes(pepsin,trypsin,amylase, lipase)during embryonic development of Procambarus clarkii.The results showed that all four digestive enzymes display different activity pattern.Pepsin specific activities was the highest in the fertilized eggs stage,and it was in the middle level in last stage.Trypsin specific activities was the highest in the egg-nauplius stage,and also it was in the middle level in last stage.Amylase specific activity changed as upside-down "V" pattern,it reached irs high values in third stages.As a whole,lipase specific activities showed relatively low values,the highest point was only 0.028±0.0007 U/mgprot.The content of dissolvable protein had a decreased trend with the development of embryos.The results suggest that the vitality of digestive enzymes fluctuate with the embryonic development,The proper time expression of digestive enzymes is correlative with the formation of the tissues,organs and systems and also supports substances and energy for the feeding of larvae.