Study On Fertilization Cytology In Distant Hybridization Between Oreochromis Aurea (♀) And Siniperca Chuatsi (♂) And Some Biology Traits Of Hybrid Offsprings

Distant hybridization is defined as a mating that was performed on interspecific, intergeneric, inter-subfamily and more distant kinship organisms. There were a variety of applications on distant hybridization of fish. Many studies about distant hybridization of fish were performed in the past. However, most of these studies focused on inter-subfamily, intergeneric and interspecific hybridization. A few successful interfamily and interorder hybridizations of fish were reported. Oreochromis aurea and Siniperca chuatsi belong to different families. From 2001, the hybridization between them was performed successfully. Up to now, a series of hybridization offsprings including the third filial generation(F₃) have been obtained. To test the insemination mechanism of distant hybridization and the influence of parents to offsprings' biological traits, we investigated the fertilization cytology of hybridization between O. aurea(♀) and S. chuatsi(♂), as well as the differences of genetic constitutions, gene express, haematological components and nutrient components between offsprings and parents were studied. The results were as follows:1,The insemination biology in hybridization between O. aurea(♀) and S. chuatsi(♂) reveals that the sperm of S.chuatsi can enter the egg cytoplasm of O. aurea, then grow into spermaster and finally form the male pronucleus. After a while, the female and male pronucleus contact and fuse each other, and ultimately become zygote nucleus. Although the hybridization between O. aurea(♀) and S. chuatsi(♂) is distant, this study shows that the whole process obeys the normal fertilization process and cleavage.2,The research investgated the genetic relationship between offsprings of O. aurea(♀)×S. chuatsi(♂) and their parents by using RAPD and sequencing methods showed percents of polymorphic loci of 5. chuatsi, O. aurea, A(F₁ of O. aurea×S. chuatsi), B(backcross between A and male of O. aurea) and C(self-cross of B) group were 19.32%,15.30%,41.33%, 29.80% and 32.31%, respectively. The genetic identity between A, B, C group and S. chuatsi were 0.3434, 0.2937, 0.3287, the genetic distance were 1.0689, 1.2251 and 1.1125, respectively. Genetic identity between three offspring groups and O. aurea were 0.9037,0.9168,0.9225, genetic distance were 0.1013,0.0869 and 0.0807, respectively. One primer could be amplified into 1 specifically RAPD band on A, B and C group which was the same as that of S. chuatsi and did not exist in O. aurea. This band was 362 bp. The sequence identity of this band was 100% between in offsprings and in S. chuatsi. We concluded some genetic substances of father were induced into offsprings of hybridization, and made the genetic constitutions of offsprings more polymorphic and closer to the father. Furthermore, these genetic substances could transfer to the next generation. However, because of backcross between A and O. aurea and self-cross of B, the genetic constitutions of offsprings were closer to the mother.3,The research that isolated the differential expression gene between offspring of Oreochromis aurea×Siniperca chuatsi and O. aurea using SSH(Suppression Subtractive Hybridization) method revealed there were differential express amounts in some genes between offspring and O. aurea, however, no new gene was detected in offspring. Although some genetic substances of father entered hybrid offspring, we concluded these substances were some DNA fragments, which can lead some expression differences of offspring's genes. However, no entire functional genes were entered into.4,A research, which focused on the haematological influence of distant hybridization by comparison on 9 haematological parameters and 7 biochemical indices of hybrid offsprings(F₂ and F₃) between O. aurea(♀)×S. chuatsi(♂) and their parents was performed. The results showed many differences significant were detected between offsprings and parents. And, not only F₂ but also F₃ had a same haematological difference pattern from parents, which there were less different indices between offsprings and mother than father. Moreover, a investigation between Egypt and Center O. aurea strain hybrid offsprings showed Egypt offsprings had more differences to mother than Center offsprings. We concluded these haematological differences were produced becaused of some hybrid effects on genetic constitutions of offsprings. And, these effects maybe help to improve the immunity, disease-resist traits of offsprings.5,Comparison on the ratio of flesh and nutrient components between F₃ offspring and O. aurea and S. chuatsi was performed. The results showed the ratio of flesh of F₃ generation was lower significant than O. aurea. Crude protein content of F₃ generation was higher than O. aurea significant, and the inverse was on the crude lipid. Four kinds of delicious amino acids(DAA) of F₃ offspring were higher than O. aurea, and the total DAA was higher significant. Furthermore, the other amino acid contents and essential amino acid index of F₃ offspring were intermediate between that of O. aurea and S. chuatsi. We concluded some effects of hybridization had shown to improve the flesh quality.Summarily, although O. aurea and S. chuatsi belong to different families, a normal insemination pattern between them was taken place. Furthermore, there were some influences of parents to hybrid offsprings, consequently, these influences lead to some differences of offsprings including haematological indices, nutrient components from parents. It can discover the mechanism of this family hybridization and select breed the offspring groups by investigating the influences of parents to offspring and the effect of heterogenous genetic substances.