Study On The Sex Determintion,Sex Ratio Of Cultural Population And Morphological Differences Between Genders Of Half-smooth Tongue Sole Cynoglossus Semilaevis

The half-smooth tongue sole Cynoglossus semilaevis is a marine species that belongs to the Pleuronectiformes order, Cynoglossidae and Cynoglossus family. This species distributes mainly at the offshore area of the Yellow and Bohai Sea, with the features such as small motion range, big body size, fast growth and delicious taste. Usually, the females grow2-4times faster than the males. The male can not reach specification of goods, therefore, along the growth of the juvenile fish, the small were picked out in order to obsolete the male. Meanwhile, the proportion of the male is much more than the female in cultured population. Some studies were carried out due to those problems.In the first half of this thesis, the sex determination mechanism of half-smooth tongue sole was inferred. Blastula and sarcomere stage embryos, and2-day post fertilization larvae from both meiogynogenesis and mitogynogenesis treatments were analyzed with a sex-linked marker, CseF-SSR. In the second part, I studied the sex ratio both genetically and morphologically in the cultural fingerlings. In the last part, the growth differences between phenotypic females and males were compared. The main results are:(1) The embryos of mitogynogenesis group died at the blastula stage totally, while the meiogynogenetic embryos can hatch. In the40mitogynogenetic blastula stage embryos,5embryos had218bp of the CseF-SSR marker, while the other embryos had the206bp band. Six of40meiogynogenetic embryos had218bp band and others had206bp band. Sarcomere stage embryos and2-day post fertilization larvae from mitogynogenesis group all had206bp. These results indicate that the half-smooth tongue sole has a female heterogametic sex determination system, which the females can spawn two different kind of gametes.(2) Genetically, the sex ratio was45.5%to54.5%, about1:1between females and males, with no significant difference. But morphologically, the male ratio was75.2%, more than the female ratio24.8%. Among the genetic females,54.3%of them had ovaries, while46.5%of them had testes, and were called as neo-male. The genetic males all had testes, no sex reverse happened. The ratio of neo-male was about21.2%in the population.(3) The6-month-old half-smooth tongue sole females and males had significant differences (P<0.05) in the body weight, and the differences became bigger when they were older than6-month-old. In body length, there were differences between6-month-old females and males, and became significantly at8months post hatching (mph). The phenotypic females were significant (P<0.05) longer and heavier than the normal males in both body length and weight after6mph. The body length and weight of neo-males were longer and heavier than the normal males, while shorter and lighter than the phenotypic females after6mph, but both differences did not reach significant level.