A Preliminary Comparative Study On Growth And Reproductive Molting Of The Ridgetail White Prawn Exopalaemon Carinicauda

Exopalaemon carinicauda is one of the most important economic shrimp in the coastal area of China,has the characteristics of long breeding season,short breeding cycle etc.During the breeding season,the female shrimp’s ovary can continue to develop which with eggs.After the incubation of the larvae,it can mate for the second time,so the female shrimp can mate repeatedly.Because there is no seminal vesicle structure in female shrimps,so mating is necessary before every spawning.The molting before the maturation of the ovary which is called growth molting and the molting before mating which is called reproductive molting.In consideration of the difficulty of synchronous maturation,artificial control of mating and rearing techniques are still not improved completely of E.carinicauda.Most of the seeds come from the natural breeding of wild broodstock,E.carinicauda artificial breeding technology still needs further study.The maturation,mating and molting of female shrimp are closely related.The comparison of the growth molting and the reproductive molting,the relationship between ovarian developmental regulation system and regulation of the molt system can provide important information for the crustacean molting mechanism,and also provide a theoretical basis for the synchronous maturation of the female shrimp and artificial breeding.In this paper,we studied the growth molting and the reproductive molting of E.carinicauda for the first time,the main results are as follows:In order to study the differences between the growth and reproductive molting of E.carinicauda,we analyzed the differences of the representative stages(Intermoult C,Premoult D,and Postmolt AB)of the two types molting from three aspects: the ecdysone concentration(MH),the molting related enzyme(CHITINASE)and non-specific immune indexes(PO,SOD,ACP,AKP).In the different stages of the growth molting,the CHITINASE activity and MH hormone concentrations had the same trend in that they gradually increased,and the difference of the stages was significant.During the reproductive molting,they decreased at first and then increased,and the differences of the stages were significant.During the intermoult and premoult stages,the CHITINASE activity and MH hormone concentrations of the growth molting was significantly lower than those of the reproductive molting,while during the postmoult stage those of the growth molting were significantly lower than those of the reproductive molting.The PO activities in different stages of the growth molting had no significant difference,while in the reproductive molting it decreased at first and then increased and showed significant differences among the different stages.In the intermoult stage,the PO activities of the growth and reproductive molting were not significantly different;in the premoult stage,the PO activity of the reproductive molting was significantly lower than that of the growth molting,and in the postmoult stage,the PO activity of the reproductive molting was significantly higher than that of the growth molting.In the growth molting,the SOD activities in the three stages gradually increased,and demonstrated significant differences.During the reproductive molting the SOD activity of the postmoult stage was significantly lower than that of the other two stages,and the difference between the intermoult and premoult stages was not significant.In the intermoult stage,the SOD activity of the reproductive molting was significantly higher than that of the growth molting.In the premoult stage there was no significant difference between them,while in the postmoult stage,the SOD activity of the reproductive molting was significantly lower than that of the growth molting.In the growth molting,the AKP and ACP activities of the three stages had the same trend in that they increased at first and then decreased,and the difference was significant.Those activities during the reproductive molting had the same trend as those during the growth molting.However,the activities of the three stages during the growth molting were significantly higher than those during the reproductive molting.The paper conducted an initiative study over the growth and reproductive molting.The results showed that there was significant difference between the growth and reproductive molting because of the ovary development.In the process of ovary development,the immunity of the body was significantly increased,and the levels of CHITINASE and hormones were decreased,which provides the theoretical basis and scientific grounding for the research on the mechanism of the molting and artificial reproduction.In order to study the role of E.carinicauda E75 gene in the process of molting.In this study,a cDNA encoding the E75 nuclear receptor of E.carinicauda was cloned using RT-PCR and RACE,named EcE75(GenBank accession number: KY471317).The full-length cDNA of EcE75 was 3944 bp,which contains a 2520 bp open reading frame(ORF)encoding a protein of 839 amino acids.The estimated mass of the deduced amino acid sequence of EcE75 was 92.307 kDa and the calculated theoretical pI was 7.48.The ZnF_C4 and the HOLI domains were detected in EcE75,and one distinct transmembrane helix was found in EcE75.The EcE75 gene is conserved in evolution.The phylogenetic tree constructed based on E75 sequences showed that EcE75 was clustered in the same clade with the crustaceans.E.carinicauda has the highest homology of Fenneropenaeus chinensis,Portunus trituberculatus,Litopenaeus vannamei and Gecarcinus lateralis.Tissue distribution analysis showed that EcE75 transcript was widespread among 13 kinds of tissues and relatively abundant in eyestalk,and ovary.According to the expression of this gene in different tissues during different molting stages,the eyestalk and the gill are consistent.The highest expression was in the premolt stage,the second was in the intermolt stage,and the lowest was in the late postmolt.So,it can be concluded that the E75 gene has a regulatory effect on the molting of E.carinicauda.Using the RT-PCR,we studied the expression patterns of ECR,RXR,E75,FAMeT genes during different growth molting and reproductive molting stages.The expression patterns of RXR,ECR and E75 gene were consistent in different stages of molting.In the premoult and postmoult stages,the expression of the reproductive molting was significantly higher than that of the growth molting.It may be the stimulation effect of ecdysone on vitellogenesis,while the activity form of ecdysone requires a combination of ECR and RXR formed two dimers resulting in the high expression.The expression of RXR gene in postmoult stage of the reproductive molting is higher than that in the premoult stage,which may be due to the development of ovary.The results showed that there was significant difference between the growth and reproductive molting because of the ovary development,the effect of the ecdysone’s stimulation on ovarian development through the upregulation of the ECR,RXR and E75 genes’ expression can be reflected.However,there was no significant difference in the expression of E75 in the premolt stage and the intermolt stage of the growth molting.It is not clear that the expression of E75 is inconsistent with ECR and RXR,which needs further study.The expression of FAMeT in reproductive molting was significantly higher than that of each stage of growth molting.The regulation effect of MF on reproduction was greater than that of growth.The higher expression of FAMeT in the premolt stage of reproductive molting is fully proved that it is a kind of gonadotropin,which can promote the development of oocytes.The study on the expression of E75,ECR,RXR and FAMeT genes in different molting stages showed that the expression was up-regulated to promote the development of ovary and molt with the development of the ovary,which provides the theoretical basis and scientific grounding for the research on the mechanism of the molting and artificial reproduction.