| Dojo loach(Misgurnus anguillicaudatus)and large scale loach(Paramisgurnus dabryanus)belongs to Cobitidac,Cobitinae,Misgurnus and Paramisgurnus,respectively.They are two economic loach in China and distributed widely.Both species are nutrient-rich,high-protein and low-fat economic fishes.M.anguillicaudatus has a variety of ploidy types and complex gametogenesis mechanism.In this study,four progeny populations were obtained from self-crossing and reciprocal crossing experiments between diploid M.anguillicaudatus(2N=50)and P.dabryanus(2N=48).Morphological differences,gonad development and differentiation and expression of gonad development-related genes were compared between hybrid progenies of M.anguillicaudatus and P.dabryanus.1.Hybridization test between M.anguillicaudatus and P.anguillicaudatus and comparison of growth differences of their progeniesIn this study,all progenies of M.anguillicaudatus,P.anguillicaudatus and their hybrids showed equally high fertilization rate,hatching rate,survival rate and low deformity rate in early life.The progenies of P.dabryanus as female parent grew faster than M.anguillicaudatus as female parent,which indicated that P.dabryanus had greater growth advantage.2.Comparison of morphological characters between hybrid progenies of M.anguillicaudatus and P.dabryanusIn order to distinguish the morphological differences between the two kinds of hybrid loaches and their parents,we observed the appearance differences,determined morphologic data and analyzed meristic and metric characters with statistical method.The results showed that the appearance of two hybrids was similar,which integrates their parental characteristics.The well-developed caudal fold of two hybrids was similar to P.dabryanus,while the pattern was similar to M.anguillicaudatus,mostly with circular spots and a few stripes.The body shape of hybrids was in between their parents,which was rounder than P.dabryanus.Cluster analysis and principal component indicated that the morphology of both species of hybrid loach was similar to each other,more resembled to P.dabryanus.The total successful discrimination rate for four loach groups by stepwise discriminate analysis was 94.1%.Furthermore,hybrid and pure groups showed the same level of hatching,normal and survival success(P >0.05).3.Histological comparative study on gonad differentiation and development of four loach progeniesHistological analysis indicated female gonad changes in pure groups at 15 days after hatching(dah),3 weeks earlier than testis differentiation.The similar results revealed that ovary formation(35 dah)priors to testis formation(80 dah).In contrary,ovarian and testicular development were differentiatal simultaneously at 35 dah and formation at 80 dah in hybrid groups.In adults,hybrids existed mature gametes,although they seemed to have less reproductive ability than parental species.The consistent results of gene expression and histological analysis revealed that gonad development of hybrids was retarded than parental species.4.Specific expression of Dmrt1 s and cyp19 s genes during gonad differentiation and development in four loach offspringIn this study,gonad development and differentiation of pure and hybrid groups were investigated.The expression of genes(dmrt1a,dmrt1 b,cyp19a1a and cyp19a1b)related to reproductive regulation was examined in adults and during ontogenesis.Both cyp19a1 a and dmrt1 s were expressed in the ovary and testis but showed sexual dimorphism.Furthermore,cyp19a1 a and dmrt1 a significantly higher expressed in pure groups.During gonad development,the exact timing of dmrt1 s and cyp19a1 a expression varied between groups.In general,their expressions were correlated to the differentiation and formation of testis and ovary respectively. |
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