Study On Artificial Breeding Technique And Hereditary Characteristic Of Spotted Halibut, Verasper Variegatus

In recent years, spotted halibut (Verasper variegatus, Temminck et Schiegel) is being paid more and more attention to in marine culture. Spotted halibut with rich nutrition is of high value in the market. However, there is yet lack of enough fishing quantity of spotted halibut due to the shortage of its natural resources. Spotted halibut breeding is very difficult to handle by manual ways, so there are not enough seeds for man/researchers to culture. Therefore, we tried to study on the hereditary characteristic of spotted halibut in order to find out the biological and genetic characteristics of spotted halibut. We also analyzed the nutritional composition of spotted halibut. This study aims to supply reference data to protect germ plasma resources of spotted halibut. We put a lot of effort to the study of the breeding techniques of spotted halibut through artificial approach , so that spotted halibut fry may be cultured in quantity as soon as possible . If the fry of spotted halibut that can be propagated come to a certain amount , then the artificial propagation of spotted halibut in marine water could be possible . The domains of our research are as follows:1.Biological characteristic of spotted halibutEvery fish has its own specifically biological characteristic. We studied on the natural distribution of spotted halibut in the sea and investigated its migration rule in the sea. The external configuration as well as the internal configuration characteristics of spotted halibut were thus observed and described. In order to find out the living habits of spotted halibut ,we analyzed the food sort in its stomach, observed the ways that it prey on animal and measured its capacity of eating. As to growth characteristic, we compared the relationship between body length and avoirdupois of spotted halibut. We also observed its spawning habit and measured its potential spawning quantity.Since the spotted halibut resource is quite rare, sampling is very difficulty in the studying course. So it is unavoidable that some studies are not so satisfying due to the lack of enough samples as well as our limited time. Some research data need to be further perfected to make our conclusion more scientific and closer to the nature of itself.2. Artificial breeding technologyIn order to breed spotted halibut by manual ways in quantity, we studied how to culture parent fish of spotted halibut in concrete pond. We changed the water conditions to observe fish's sex gland developing and used the synthetic technique to control the parent fish's sex gland developing. When the parent fish's sex gland developing is mature, we inject hormone into its body to promote its spawning and used artificial insemination to obtain zygote.After three years' study and observation, we have come to make clear the rule of spotted halibut sex gland developing and the appropriate water temperature for its parent fish spawning. Using the synthetic technique ,we are now able to control the parent fish sex gland developing successfully and have obtained zygote continuouslly in these three years by artificial insemination.Through observation and contrast, we have known the morphological changes in its early stage as well as the developmental characters of embryo of spotted halibut. We found out the appropriate conditions for the embryo of spotted halibut and made the fry hatched successfully from zygote. We observed the metamorphism growth of fry and juvenile of fish and can breed some fry into juvenile of fish.At present, however, we cannot make matured parent fish of spotted halibut into spawn naturally yet. At the same time, due to the lack of enough quantity of parent fish of spotted halibut, the good zygote is not abundant for fry breeding in large amount, so there isn't enough juvenile fish for marine culture at the moment. Henceforth, our key work focuses on how to make matured parent fish of spotted halibut spawn naturally and obtain enough zygote for fish breeding through artificial approach.3. Genetic charactersGgenetic characters of fish germ plasma mainly concern chromosome, DNA and isoenzyme.Partial nucleotide sequences of Mitochondrial Cytb, ND5, COI, and 16S rRNA genes were determined and analyzed for Verasper variegatus and V. moseri. Eighty —three nucleotide substitutions were detected between the two species in the total 2056 bp sequences analyzed, most of which were synonymous transitions at the third codon positions. Nucleotide composition analysis has revealed that the two species investigated showed a strong bias against guanine (G) in the three protein-coding genes and particularly at the third codon positions, the 16S rRNA gene showed an even nucleotide distribution of the four nucleotides. There was apparent difference on the degree of genetic divergence between the two species in different mitochondrial gene segments and the nucleotide substitution rates arranged from high to low were Cytb>ND5>COI>16S rRNA.The karyotype of spotted halibut ( Verasper variegates) was examined by the PHA injection method. The karyokinesis index is 1.3%, metaphase Karyokinesis posture is good. The karyotype formula of spotted halibut is 2n=44t, the chromosome number of spotted halibut is fewer than that of other flatfish.4. Nutritional valueThe main nutritional elements and their contents in spotted halibut were analyzed and evaluated tentatively, i.e. the different kinds and contents of amino acid, content of unsaturated fatty acid, contents of constant and trace elements.In general, spotted halibuts share the same merit as the other flatfish, their entrails are comparatively smaller and their meat content is relatively richer. The value of protein in spotted halibut is higher than that of flounder, because the collagen content in the muscles of spotted halibut is larger than that of flounder, and there are abundant of dissociation amino acid in spotted halibut muscle as well.Nevertheless, the work we have done in this study can hardly be more than tentative. Problems and limitations are unavoidable . Some of them may have escaped the writer's recognition , and some are recognized yet unsolved. For example, due to the difficulties in obtaining enough samples ,apart from our restricted time and energy, some research data need to be further perfected . therefore, we still have responsibility to broaden the scope of our research to speed up the process of artificial propagation of spotted halibuts.