Hybrid breeding procedures and methods for fish

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 (for example, hybrids of carp and white peony).

The breeding process is to select the individuals that meet the breeding objectives in the breeding types of the hybrids 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 the variety and production, and it is one of the basic approaches for fish breeding. It is also an effective measure for the breeding of high-quality fish species by the hybrids of carp and carp.

The most common applications in crossbreeding are crossbreeding (referring to hybridization between two cultivars), followed by distant hybridization (hybridization between different species and individuals). Practice has shown that hybridization between varieties, such as cockroach and salmon, cannot be widely used in the production field. The key is the result of the instability of post-hybrid combination traits.

The traits of the hybrids of carp and carp are not good traits. There is no difference in the growth rate and bait coefficient from one-year-old fish breeding with carp and carp, but there are obvious differences in the second-instar growth period, and the growth rate is slow and individual Small, seriously affecting production. It can be seen that not all crosses can create good varieties.

Formation and Utilization of Heterosis

The hybrid germplasm superiority refers to the first generation of hybrids produced by the cross of two parents with different genetic compositions and is superior to their parents in growth potential, viability, fertility, resistance, yield and quality.

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, ecotypes and physiology, the better the relative traits of the parents can complement each other; the stronger the heterosis, the higher the degree of homozygosity of the parents, and the more consistent the hybrid Advantage.

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 crossbreeding of fish is the most widely used economic hybrid. If the second generation is allowed to self-cross or continue to mate with its generations, the heterozygosity will gradually decrease and the heterosis will decline or even disappear.

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 seedlings of the genus Polygonaceae and the lotus seedlings that have been approved by the National Pedigree Research and Approval Committee have [the purse-red peony (female) Yuan Jiang Ye (Xiong)] and the Feng Yu [Xingguo Jing 鲤 (Female) Scattering Mirror 鲤 (Hung)] The use of hybrid germplasm, such as hibiscus 散 散 散 兴 兴 兴 兴 兴 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 鲤 可以 可以 可以 可以 可以 可以 可以 异 异 异 异 异 异 异 异 异 异 异 异Strong, strong disease resistance, high survival rate, high aquaculture production, excellent quality and other economic advantages.

Hybrid breeding technology

The selection of parents is the key. First, parents should use parents with good comprehensive traits, many advantages, few defects, or good traits that can complement each other. At the same time, parents should pay attention to the selection of parents with relatively different ecological types, such as heterotrophic silver. He is the earliest parent of the natural gynogenesis of the Shuangfeng Reservoir in Fangzheng County of Heilongjiang Province as the female parent, and the heterogenous triploid gynogenesis obtained from the hybrid father of Xingguohongjing in Jiangxi Province. The offspring have obvious advantages in growth speed.

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.

Single cross: The cross between two cultivars (single cross) is denoted by xy, and the hybrid germplasm progeny becomes a first-generation hybrid, for example, the germplasm of the hybrid of Xingzheng (female) 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.

Hybrid hybridization: two or more varieties, breeding methods that have been crossed twice or more. 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).

Backcrossing: The hybrid offspring continue to crossbred with one of their parents in order 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.

Hybridization procedures and methods

Preparation before hybridization: First of all, 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.

Choose the appropriate fertilization method for hybridization: At the beginning of the pre-hybridization and the coming of the reproductive season, the male and female fish must be kept in separate ponds to avoid 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.

Records, Signs, and Management: Hybrids of different species of fish must be recorded or registered. The records include parental traits and relevant conditions, such as hybridization methods, hybridization time, fertilization rate, survival rate, etc. 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 you inadvertently exile a hybrid into rivers, lakes, and other natural waters, it will cause serious consequences of the genetic mixture of natural populations and seriously affect the effective use of natural resources.

Accelerating the breeding process: From hybrids to the breeding and promotion of new varieties, it often takes 10 generations, so it is necessary to speed up the breeding process. This method can be used to speed up the breeding process. It can be used in different places, or in greenhouses and artificial climates. If the required breeding base is not large enough, this method can speed up the breeding process.

Selection of hybrid offspring: When using the individual selection method, the selection generally starts from the second generation of the second generation. The second generation of factor variation has the largest range, and it is expected that the desired variant can be selected from it, and the second generation can basically judge the hope of breeding the variety. . 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 have laid a good foundation for the production of pollution-free fish.

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