Analysis Of Reproductive Traits In Several Cultured Populations Of Litopenaeus Vannamei

Litopenaeus vannamei has the advantages of fast growth,low nutritional requirements,high disease resistance and high meat yield and so on.It is an excellent breed of intensive culture.The broodstock is at the top of the whole industrial chain of Litopenaeus vannamei.Most of the Litopenaeus vannamei broodstock in China are directly introduced from abroad or produced by the expansion and breeding of imported populations.The dependence on foreign broodstock seriously restricts the healthy development of the industry of Litopenaeus vannamei in China.Therefore,it is necessary to introduce Litopenaeus vannamei broodstock and establish an independent breeding system through cross breeding.The morphological characteristics of Litopenaeus vannamei are related to growth and reproduction,and the morphology of different culture populations is different.Therefore,it is of great significance to explore the relationship between morphological characteristics and reproductive traits for the breeding of high fecundity species of Litopenaeus vannamei.There are some differences in breeding traits among different culture populations,and the reproductive performance of different individuals is also different.The reproductive performance and larval development of different populations of Litopenaeus vannamei were compared by one-way ANOVA,and the relationship between morphological characteristics and reproductive parameters was discussed by correlation analysis.In addition,the differences of biochemical components in different tissues of female shrimp with different spawning intervals were also studied.The results provide reference data for breeding new Litopenaeus vannamei varieties.The main results are as follows:1.Comparative analysis of breeding characters of different culture populations of Litopenaeus vannameiIn order to evaluate the reproductive performance and larval development of female shrimps from different breeding populations,371 female shrimps from three breeding populations and their offspring of 103 families were selected in 2019,and307 female shrimps from three breeding populations and their offspring of 146families were selected in 2020.The mating rate,egg numbers,hatching rate and other reproductive parameters of each female shrimp were recorded during the production period,and the larval development data such as metamorphosis duration and survival rate were recorded.20000 nauplii were selected from each family to track their larval metamorphosis and larval development.The results showed that S population/fast-growing population was the lowest in mating.The hatching rate of P population/high-resistance population was the lowest,and the hatching rate of Ecuador was the highest.In terms of spawning,the relative egg numbers of Ecuador population,fast-growing population and P population were higher;The spawing interval of Ecuador population was the smallest,and that of P population was the highest（P<0.05）.By analyzing the data of larvae development in 2019,it can be seen that compared with the other two populations,the survival rate of Ecuador population is superior.Based on the analysis of larval development data in 2020,it was found that the larvae of Ecuador population had superiority in metamorphosis duration The results showed that the breeding performance of different Litopenaeus vannamei populations was different.In addition,this study also found that there was a significant positive correlation between body weight and egg numbers（P<0.01）,and the correlation coefficient was 0.396.2.Relationship between breeding traits and biochemical components of Litopenaeus vannameiIn order to compare the biochemical components of eggs,hepatopancreas and ovaries of female shrimps at different spawning intervals,three groups were designed in the experiment:short spawning interval group（<3 d）,medium spawning interval group（3-7 d）and long spawning interval group（>7 d）.There were 9 individuals in each group.In order to explore the differences of biochemical components of different hatching rate and different survival rates（N_Ⅰ→P₁）of eggs,three groups were also set up,which were low hatching rate/survival rates（N_Ⅰ→P₁）（<30%）,medium hatching rate/survival rates（N_Ⅰ→P₁）（30%-70%）and high hatching rate/survival rates（N_Ⅰ→P₁）（>70%）.There were 9 individuals in each group.The results showed that the contents of triglyceride and vitellin in the first spawn eggs of Litopenaeus vannamei with low spawning interval were often higher,so the contents of triglyceride and vitellin could be used as the prediction index of whether Litopenaeus vannamei could spawn many times.The contents of C12:0,C14:0,C14:1,C20:5n-3,C22:0 and C22:6n-3 in the first spawn eggs of female shrimp at different spawning intervals were significantly different（P<0.05）.The results showed that there was no significant difference in the activity of alkaline phosphatase and acid phosphatase in the first spawn eggs of Litopenaeus vannamei at different spawning intervals（P>0.05）.There were no significant differences in the contents of total lipid,total protein,cholesterol,protease,lipase,alkaline phosphatase and acid phosphatase in the ovaries of female shrimp at different spawning intervals（P>0.05）,but the contents of triglyceride in the ovaries of female shrimp with spawning interval less than 3 days were significantly higher than those with spawning interval more than 7 days（P<0.05）.The results of fatty acid analysis showed that the contents of C18:2n-6,C22:6n-3（DHA）,n-3 and n-6 series fatty acids in the ovaries of female shrimp at different spawning intervals were significantly different（P<0.05）.The ratio of n-3/n-6 was higher in the ovaries of female shrimp with spawning interval（3-7d）（P<0.05）.There were no significant differences in the activities of total protein,total lipid,triglyceride,protease and lipase in hepatopancreas of female shrimp at different spawning intervals（P>0.05）.However,the cholesterol content in hepatopancreas of female shrimp at spawning intervals of 3-7 days was significantly higher than that of hepatopancreas of female shrimp at spawning intervals of less than 3 days and more than 7 days（P<0.05）.The results of fatty acid analysis showed that the content of monounsaturated fatty acid of female shrimp at different spawning intervals was significantly different（P<0.05）,and the content of monounsaturated fatty acid of female shrimp with short spawning interval（>3 d）was lower.The contents of total lipid,total protein,triglyceride,cholesterol,carotenoid and vitellin in eggs of Litopenaeus vannamei with different hatching rate and survival rates（N_Ⅰ→P₁）had no significant difference（P>0.05）.There was no significant difference in the activity of alkaline phosphatase and acid phosphatase between eggs with different hatching rates（P>0.05）.However,the content of C20:4n-6 in eggs with different survival rates（N_Ⅰ→P₁）was significantly different（P<0.05）.The content of C20:4n-6 in low survival rates（N_Ⅰ→P₁）（<30%）was about 20%higher than that in high survival rates（N_Ⅰ→P₁）group（>70%）.In conclusion,in the production and breeding period of Litopenaeus vannamei,we can predict whether Litopenaeus vannamei broodstock can spawn many times in a certain period of time according to the contents of triglyceride and vitellin in the first spawn egg of female shrimp.