The Study On The Development Period Of Fertilized Eggs And The Influence Of Environmental Factors On The In Vitro Hatching Of Crayfish

Procambarus clarkii,commonly known as crayfish,is popular among all age groups because of its good taste and high nutritional value.With the development in recent years,it has become one of the important economic varieties of freshwater aquaculture in China.In recent years,due to the rising income level of the people,the demand for high quality and high nutrition of food materials in the market,the market share of Procambarus clarkii has been rapidly expanded,and the scale of aquaculture has also been expanding.However,in the process of aquaculture,the supply of seedlings has become the main bottleneck of the scale of aquaculture,especially in recent years,due to the impact of climate change,overfishing,habitat environment and so on,the wild seedlings are growing rapidly The production of crayfish has declined seriously,but the production and specifications of crayfish seedlings obtained by soil pond and greenhouse can not meet the increasing demand.The large-scale industrial breeding method of artificial eggs hatched in vitro with fertilized eggs of Procambarus clarkii has become a new response.This study redefined the developmental stage of fertilized eggs of Procambarus clarkii by means of microscopic examination,so as to provide the basis for large-scale and controllable in vitro culture of Procambarus clarkii seedlings.The effects of basic environmental conditions such as different temperature,salinity,do,water flow velocity and trace elements in water environment on embryo development of Procambarus clarkii were studied to explore the mechanism In order to meet the basic requirements of industrial production,the optimal environment for in vitro incubation of fertilized eggs of Procambarus clarkii was studied.The main work of this paper is as follows1.Determination of the developmental stages and nutritional indices of the fertilized eggs of Procambarus clarkiiIn this study,the fertilized eggs of Procambarus clarkii were obtained by artificial stripping from the culture pond.Through the observation of external morphology and microscopic structure,the more obvious and easy to identify each stage of the development of fertilized eggs were obtained.At the same time,the nutritional composition of embryos in each stage was determined.It can be divided into six stages by naked eye:the first stage is from fertilized egg to cleavage stage,the second stage is from blastocyst to gastrula stage,the third stage is prophase of nauplius,the fourth stage is anaphase of nauplius,the fifth stage is pigment stage of compound eye,and the sixth stage is ready for hatching.At the same time,the basic nutritional indexes of each period were determined.It was found that the water content of Procambarus clarkii embryos increased gradually with the development of Procambarus clarkii embryos,while the protein content,fat and carbohydrate content decreased,indicating that the changes of nutrients in Procambarus clarkii embryos were consistent with those in other crustacean aquatic animals.2.Effects of different environmental conditions on the development of fertilized eggs and in vitro incubation of Procambarus clarkiiIn this study,the fertilized eggs of Procambarus clarkii were separated from the parent shrimp in different environmental conditions,and different parameters were set,such as temperature,salinity,do,water flow velocity,and trace elements.The optimal incubation conditions of the fertilized eggs of Procambarus clarkii were obtained through the incubation rate and survival rate of the fertilized eggs The best initial period of in vitro hatching of fertilized eggs of Procambarus clarkii was obtained through the final hatching survival rate and hatching rate of fertilized eggs in different periods.It was found that the optimal water environment for the development of in vitro fertilized eggs was 28℃±0.5℃,DO 6±0.5 mg/L,salinity 2‰-4‰,and water flow rate 40±0.5 cm³/s.At the same time,the experiment found that the appropriate amount of trace elements in the water also had a significant role in promoting the hatching of shrimp embryos.When the concentration of Ca²⁺was 30-60 mg/L,the concentration of Mg²⁺was 0-30 mg/L,and the concentration of Zn²⁺was 0-5 mg/L,the hatching rate of fertilized eggs was improved to a certain extent.But Cu²⁺has obvious lethal effect.The results show that the fertilized eggs of Procambarus clarkii can be hatched in vitro in the artificial environment,The time of fertilized eggs in vitro of Procambarus clarkii is in the third or fourth stage,and the high hatching rate of fertilized eggs in this stage has the significance of industrial production.