Hybrid breeding techniques for farmed fish

First, the significance of cross-breeding Breeding good varieties by hybrid methods, or use heterosis called cross-breeding. Hybridization can shift the genetic material of organisms from one group to another, which is an important method to increase biological variability. Different types of parents can be crossbred to obtain recombination of variation traits. Combinations of good parental traits may appear in the crossbreds, and even the superior traits of the parental parent (for example, the combination of Fongzheng Yinzhi and Jiujiang Hongqi) may occur. Of course, parents may also appear. The advantages are not obvious trait combinations, or inferior traits that are not found in both parents (hybrids of salmon and white peony). The breeding process is to select individuals that meet the breeding goals in the repeated types of hybrid offspring to further cultivating, and even obtain new varieties with good traits.
Hybridization can increase the variability and heterogeneity of hybrid offspring, integrate the good traits of both parents, and produce new traits that are not found in some parents, resulting in greater genetic improvement in offspring and the emergence of heterotic heterosis that can be exploited in fishes. The variety play an important role in the improvement of breeds and production, and it is one of the basic approaches for fish breeding. It is also an effective measure to cultivate high-quality fish species.
The most commonly used interbreeding (crossbreeding between two cultivars) is used in crossbreeding. Followed by distant hybridization (different species, genus-like hybridization). According to the practice in this field for many years, hybridization between different breeds, such as cockroach and salmon, cannot be widely used in the production field. The key is the result of the instability of the post-hybrid combination. Whether the traits are good traits, the growth rate and feed coefficient of the first-year fingerlings are not different from those of pupa and squid, but there are obvious differences in the second-instar growth period. The growth rate is slow, and the individuals are small and severely affected. To yield and economic benefits. It can be seen that not all crossbreeds can create good varieties, and only with painstaking exploration can we achieve ideal results.
II. Formation and Utilization of Heterosis The hybrid germplasm dominance refers to the first generation of hybrids produced by the cross of two parents with different genetic compositions. Their growth potential, viability, fertility, resistance to stress, yield and quality are higher than those of their parents. Superior phenomenon. The hybrid germplasm advantage is the comprehensive performance of many traits. The size of the hybrid germplasm dominance often depends on the relative differences between the parental traits and complement each other. In general, the greater the differences in kinship, ecological types, and physiological characteristics, the relative strengths and weaknesses of the relatives of the parents can complement each other; the stronger the heterosis, the higher the degree of homozygosity of both parents, and the more consistent the heterosis can be obtained. .
The advantage of hybrid germplasm often manifests itself in economically significant traits, and thus hybrids that produce and exploit heterosis are often referred to as economic hybrids. At present, the most widely used hybrid fish breeding is economical crossbreeding. The second generation begins to gradually decline. If the second generation is allowed to self-interpolate or continue to allow its generations to freely mate, the heterozygosity will gradually decrease. Heterosis tends to decline and even die.
At present, the use of hybrid germplasm has become one of the important measures to increase production and improve quality in freshwater fishery production. At present, the hybrid germplasm of Cinnabaraceae and Rhizoma Cymbidium that have been approved by the National Pedigree Research and Approval Committee [purse red peony (female) Yuan Jiang Ye (Hung)] and Feng Ke [Xingguo Jingshen (Female) Scintillation Mirror (Xiong)], The use of hybrid germplasm, such as Hibiscus flourishing stigma (female) and rejuvenating red hawksbill (male), can bring huge economic benefits. For example, the heterotrophic silver crucian carp only grows about 60% faster than the parent, and it is also resistant to stress. Strong, strong disease resistance, high survival rate, high aquaculture production, excellent quality and other economic advantages. At present, the promotion of farming in most provinces and cities in the country is an effective way for rural farmers to increase their income.
Third, cross-breeding technology selection of parents is the key, first of all to use as far as possible the use of comprehensive traits, many advantages, fewer defects or good traits can complement each other's parents, but also pay attention to choose the larger ecological types, relatives distant parental hybridization For example, the Chinese Academy of Sciences (Biology Institute) is the first child of the Chinese Academy of Sciences (Biological Institute) to use the natural gynogenesis of the Shuangfeng Reservoir in Fangzheng County of Heilongjiang Province as the parent, and the Xingguo Rainbow Trout of Jiangxi Province as a hybrid, obtained by artificial insemination. The offspring of the heterotriploid gynogenetic development had a distinct advantage in growth rate, which was 34.7% faster than that of the Japanese silver cocoon and 2-3 times faster than that of the common cod.
The characteristics of heterotrophic silver crucian carp can fully explain the advantages of hybrid germplasm. In the breeding process, it has the advantages of wide feeding habits, rapid growth, less disease, strong adaptability, and high survival rate. It has a delicious meat, nutrient-rich, protein, The amino acid content has a certain increase compared to common squid. Large consumer groups and good market prospects.
The commonly adopted method of hybridization is the success or failure of the breeding after the parent is determined. What kind of hybrid combination method is used directly depends on the success or failure of the breeding. Usually, single cross, compound hybrid, backcross and other hybrid methods are used.
1. Cross-singling between two cultivars (single cross) is indicated by xy, and the hybrid germplasm progeny becomes a first-generation hybrid, for example, a germplasm obtained from a cross between Xingzheng Hongqi (female) and Xingguohongjing (male). Because it is simple and easy to operate, it is the most widely used in production. Generally, it mainly uses the first generation of hybrid germplasm, such as heterotrophic silver carp and lotus caraway.
2. Hybrid breeding of more than two varieties, after two or more hybrid breeding methods. If single crosses cannot fulfill the desired traits for breeding, hybrid crosses are often used. The aim is to create hybrid populations that are rich in genetic bases before they can be selected for better individuals. Hybrid hybridization can be divided into three cross, double cross and so on. Sanjiao is the re-hybridization of one single cross with another, and can be expressed as (xy)y. For example, (Bloompot, Red River, Yuanjiang River), scattered scales, = three crosses, and double crosses, which are hybridizations of two different single crosses, can be expressed as (ab) (cd) or (ac) (bc). For example, (Cryptocera hornbill) (Mozambique non-fish Nile tilapia).
3. The backcross hybrids continue to re-hybridize with one of their parents to enhance breeding methods for a parental trait of the hybrid generation. When the purpose of breeding is to attempt to introduce one or several economic traits of a group B into another group A, backcross breeding can be used. For example, squid has many good traits, but it cannot tolerate low temperatures and genetic improvement is needed. Multiple backcrosses can be conducted with Xianghuaxi tolerant to hypothermia, and the attention to backcrossing offspring selection must be focused on the cold-resistance trait so that a new carp species with excellent cold resistance can be eventually developed.
IV. Hybridization procedures and methods
1. The preparatory work before hybridization should first be familiar with the reproductive habits of various fish species. On the one hand, it is necessary to understand the habits of the fish, such as the sexual maturation season, reproductive season, egg nature, sex cycle, spawning period, and the protection of eggs and offspring; on the other hand, it is necessary to understand the fish's reproductive conditions during the external conditions. Requirements, such as water temperature, light, flow velocity, dissolved oxygen in water body, substrate of spawning ground, fish nest, feed, etc. Secondly, it is necessary to regulate the age of sexual maturation of the parents, and adopt different means such as breeding in stages to create different external conditions, so that the unhybridized parents must meet in the reproductive season.
2. Select the appropriate fertilization method for hybridization In the early stages of sexual maturation and the coming of the reproductive season, both male and female fish must be kept in separate ponds to avoid self-match mating. The method of fertilization is determined according to the specific conditions. Hybrids between breeds are generally fertilized by natural spawning, and artificial insemination cannot be used for natural breeding.
3, records, signs and management of hybridization with different species of fish, must be recorded or registered, including the contents of the parental traits and related conditions, such as hybridization, hybridization time, fertilization rate, survival rate, etc., for reference for reference. After the fish fry under the pond, the test pool needs to be listed and registered, indicating the date of fertilization and the name of the parent's book. During the cultivation period, management should be strengthened. In particular, care should be taken to avoid mixing between different impurities. If inadvertently exiled hybrids into rivers, lakes, and other natural waters; it will cause serious consequences of hereditary mixture of natural populations, seriously affecting the effective use of natural resources.
4. Accelerating the breeding process From hybridization to breeding and promotion of new varieties, it often takes 10 generations, so it is necessary to speed up the breeding process. Different generations can be used, such as the establishment of fish breeding bases in Guangdong and Hainan, etc., and northern breeding can shorten breeding time. Can also be artificial climate to greenhouse and Kayo, is not required when the size of the breeding base, using this method that can speed up the breeding process.
5. When using the selected progeny individual selection method selected from the general sub start the second generation, the maximum range of variation factor II, is expected to be desirable to choose the variant, the second filial generation basically based on the presence or absence Cultivars hope. By the time of the fifth generation, most of the traits and pedigrees were fairly stable, and the identification of the varieties could be carried out at this stage. When the population selection method is adopted, the individual is not selected before the sub-five generations, and only group selection and polyculture are performed. From the fifth generation to the eighth generation, individual selection, establishment of family lines and identification of varieties, and true selection of new varieties with good traits laid a good foundation for the production of pollution-free fish.

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