The Molecular Genetic Traits Of The Hybridization For Channa Maculata (♀) And C. Argus (♂)

Channa argus is an important economic freshwater fish. During the breeding process, it needs to be fed chilled fish, resulting in deterioration of water quality. The hybrids (C. maculata(?) and C. argus(?)) can be fed with artificial feed, which greatly reduces the harm to the environment farming. The hybrids also obtained excellent traits from its parents, which has been promoted in the production. We studied the taxonomic status of C. maculata and C. argus by part sequence of COX1gene and16S gene and full length sequence of ITS, which could be provided for the molecule basis for hybrid. And we also sequenced the whole mtDNA length for C. maculata, C. argus and the hybrid (C. maculata (?) and C. argus (?)).-By the technology of SRAP to study the genetic raltionships of C. maculata, C. argus and the hybrid (C. maculata (?) and C. argus (?)), and by the technology of SSR to research the transfer of genetic information from F1parents to F2generations. Finally, we analysised the gentic diversity for five cultured population of C. argus. The results are summarized as follows:1. The molecule basis for hybrid between C. maculata (?) and C. argus (?)Four kinds of snakehead fish were analyzed using part gene of COX1and16S. High conservative in four kinds of snakehead fish, low intraspecific variation and large differences between species were detected. The interspecific K2P distances were higher than intraspecific distances. A total of19haplotypes were identified in COX1gene in this study. And each haplotype is652bp. No insertions or deletions phenomenon were founded in this study. Under the model of K2P, the lowest interspecific distance (0.091) was between C. argus and C. maculata while the highest interspecific distance (0.219) was between C. argus and C. striata. A total of10haplotypes were obtained in16S gene in this study. The length sequence of haplotypes of C. argus, C. maculata, C. asiatica and C. striata is573bp,573bp,573bp and572bp. Under the model of K2P, the highest interspecific distance (0.077) was between C. argus and C. striata, between C. maculata and C. striata, while the lowest interspecific distance (0.021) was between C. argus and C. maculata. No overlap was found between intraspecific and interspecific distances, suggesting the existence of a distinct barcoding gap. The ML and NJ tree show all the snakehead haplotypes belong to one of the four Channa species. First, C. argus was clustered with C. maculata, then were clustered with other fish. It indicates that C. argus and C. maculata had the lowest genetic distance and the closest relationship.The length of the rDNA sequences of C. maculata and C. argus were927bp and902bp. The content of G+C (about72%) is higher than A+T. Distinct differences fragments were found between C. argus and C. maculata(particularly30bp more in ITS2of C. maculata). The interspecific K2P distances were higher than intraspecific distances. Phylogenetic analysis showed that C. argus and C. maculata (0.020) had the lowest genetic distance, while C. argus and C. asiatica (0.073) had the highest genetic distance.Minimal sequence differences and lowest distant were observed in C. argus and C. maculata. And these two fishes were latest differentiation from other snakehead fishes. These provides the molecular basis between C. argus and C. maculata.2. The complete mitochondrial genome of C. maculata, C. argus and hybridsnakehead fish [C. maculata ((?))XC. argus ((?))]The total length of the C. maculata mitochondrial DNA was16559bp, which was slightly longer than C. argus (16558bp) and hybrid snakehead fish (16558bp). The structural organization and location of different feature in the snakehead mt genomes conformed to the common vertebrate mt genome model and consisted of13protein-coding genes,2rRNAs,22tRNAs and1putative control region. There was no obviously favor base pair in third position of encoding amino acids. The CUC (193) codon was used most frequently in C. argus while the CUA (204) codon was used most frequently in C. maculata and hybrid snakehead fish. The amino acids Leu is the most frequently used encodon in C. argus (17.9%), C. maculata (17.5%) and hybrid snakehead fish (17.5%). COXl started with GTG while other PCGs genes used ATG as the initiation codon. The ATP6and ATP8shared10bp overlap, whereas ATP6-COX3and ND4L-ND4shared1and7bp overlap, respectively. TAG was the termination codon in C. argus while TAA was the termination codon in C. maculata and hybrid snakehead fish for ND5. Seven PCGs ended with TAA (ND1, ND2, COXl, ATP6, ATP8, COX3, and ND4L), one ended with TAG (ND6) and the rest had incomplete stop codon T (COX2, ND3, ND4and CYTB). This feature is common among vertebrate mitochondrial PCGs, of which incomplete stop codons are presumably completed as TAA via posttranscriptional polyadenylation.C. argus and C. maculata, as the representative of the suborder Channoidei, formed the most basal branch having a sister relationship with a monophyletic clade including the other suborders of Perciformes. These could provide some basic information for fish taxonomy.3. The SRAP analysis of C. maculata, C. argus and their hybrid [C. maculata ((?))×C. argus ((?))]The genetic structure of C. argus, C. maculata and their hybrid [C. maculata ((?))×C. argus ((?))], the heterosis of the hybrid F1, were analyzed by the SRAP technique with14primers.105loci were amplified in three population, and each combination of primers amplified bands ranging from5to10. Out of105loci,88loci occurred polymorphism band in three population, accouted for83.81%,48loci (45.71%) occurred polymorphism band in C. argus,27loci (25.71%) occurred polymorphism band in C.maculata,34loci (32.38%) occurred polymorphism band in hybrids. The H for C. argus, C. maculata and hybrids were0.1489,0.0964,0.1076, respectively. The results showed that the genetic distance of hybrids and male parent (0.2195) or female parent (0.4009) was closer than the genetic distance of male parent and female parent (0.6367), which indicated hybrids F1was the hybrid offspring produced by parents. It also indicated that the relative genetic distances were not equal (closer to male parent) between the hybrids and their parents.4. Transfer of genetic information from F1parents to F2generationsTransfer of genetic information from F1parents to F2generations were analyzed by10SSR loci in3group (90individuals). The inheritance of7loci (WL-28; CHA13; CHA25; CHA31; CHA41; CarC7; CarD139) was shown to be in agreement with Mendel’s law. However, nearly half F2offsprings had no genotypes by3loci (WL-8, CarD108and CarD121), which indicated one or several chromosomes do not exist in nearly half individuals. Combined with the number of F2offspring chromosomes44and45, indicating that there is one or several chromosomes can not pair during meiosis. During the first meiotic division, the one or several chromosomes may randomly into one cell. It then conducted the second meiotic division. In this study, the research enriched the contents of the theory of sexual reproduction of fish.5. Genetic diversity of five cultured C. argus populationA total of160alleles were detected at the ten microsatellite loci. The average heterozygosity (HE) and observed heterozygosity (Ho) varied from0.65-0.91and0.67-0.85in five cultured populations, indicating high genetic diversity in these five populations. Among them, the highest genetic diversity was observed in YJ population. Some loci in YJ, YG, LQ population deviated from H-W. Population YJ deviated from mutation-drift equilibrium and may have experienced a recent bottleneck. It is necessary to increase effective population sizes in YJ population for better breeding. No differentiation and some gentic structure between XS population and YH population, which indicated the two population were the some population. There is moderate differentiation between LQ population and other poplation. The farest genetic distance was observed between LQ population and YH population, which could be served as a good breeding strategy.