| Paralichthys olivaceus is a valuable economic marine fish in our country, whose artificial cultivation began in the1990s, and has developed into the important breeding object in north and the coast of Fujian. It is very popular in the market because of its individual size, fresh meat and the high nutritional value.In recent years, the use of artificially induced gynogenesis has successfully bred new varieties for the development of the aquaculture industry to provide a quality breeding material.Induced gynogenesis is an effective way to rapidly improve the homozygosity. Fish meiotic gynogenetic progeny of heterozygous mitotic gynogenetic homozygous offspring, namely the double haploid (Double Haploid, DH). Preparation for meiosis gynogenesis is relatively easy, however, mitotic gynogenesis preparation is much different. Meiosis gynogenesis can quickly fix the trait of female parent, and because the paternal chromosomes are not involved in the formation of zygote nuclear, the artificial induction of gynogenesis greatly reduces the process of the homozygous offspring, which also can get the varieties, possessing the superior trait, by the hybridization among different pure lines. It is called single hybrid, which provides an important method for improving the variety of fish, it has excellent hybrid vigor."Single Hybrid" approach is the primary method of breeding crops such as corn, the study created a single hybrid of paralichthys olivaceus.This study includes two parts:one is the study on the gender differentiation and gonad development of the DH paralichthys olivaceus; the other is the study on the growth and genetic characteristics of the single cross hybrid of paralichthys olivaceus. And it gets the following achievements:(1) The gender differentiation of the DH paralichthys olivaceus is later than the common fish. When the age was about30to40days, primitive germ cells increased from1to4, and constituted the gonads primordium with the genital ridge. While55days, the capillaries occurred in the sex gland, but we still can’t distinguish whether male or female. While60days, sex gland was developing to the ovaries, and lacuna was formed in the middle. While70days, spawning board was formed. While90days, the number of spawning board and oogonium increased, and cell volume further increased. While100days, the ovarian cavity is still not closed. And while110days, there were a large amounts of transition cells from oogonium to oocyte in the spawning board, the I phase oocytes did not occur.In the fish, whose ages are55days, the gonads are long strips. And when60-80days, testis continued to extend and broaden, meanwhile the spermatagonial cells increased. When90days, the seminiferous lobules were formed, and the number of the spermatagonial cells increased a lot. When100days, primary spermatocyte occurred, and there was a small amount of secondary spermatocyte, which marked the gonad differentiated completed.(2) The gonad development of the DH paralichthys olivaceus is slower than the common paralichthys olivaceus. When the age was9to11months, the testis development of the DH paralichthys olivaceus was Ⅲ stage, and the common entered into Ⅳ stage. When11months, we observed a sign that the testis of mitosis was degradation. When13to15months, the testis degradation occurred, finally developed into seminiferous lobules within spermatogonium only, and primary spermatocyte disappeared, like the testis in II stage. When16to18months, the testis of the several paralichthys olivaceus developed normally, but compared with the common paralichthys olivaceus, there was some testis still staying in II period.Compared with the common paralichthys olivaceus, the ovary, staying in II stage, developed slowly, and the most structures of the ovarian oocyte changed, which were embodied in the nucleus and cytoplasm, as long as divided into three types. We also observed the degradation and abortion of ovaries.(3) The gender ratio of the DH paralichthys olivaceus. By tissue slice observation, in the79DH paralichthys olivaceus, there are44females, accounting for55.7%of the total population;30males, accounting for37.9%;5undifferentiated fish, accounting for6.3%. That means the proportion among male, female and undifferentiated fish is about56:38:6. This is a rare biological phenomenon that there are so many males in the DH paralichthys olivaceus, which needs to be further research.(4) The average genetic similarity of single-cross hybrid is0.8261, higher than the control group(0.6727), while the average genetic similarity of gynogenesis inbred line is0.8312, slightly higher than the single-cross hybrid. The average alleles’number and the observed heterozygosity of the control group (3.25and0.9167respectively) are higher than the single-cross hybrid and the gynogenesis inbred line, mainly because the control group is a common hybrid, and progeny idiotype is a random combination of their parents, which means the types are rich.(5) Single cross hybrids grow significantly faster than the control group. Under the same cultivation conditions, when the age is110days, single-cross hybrids was more increased than in the control group for40.83%of body weight and13.18%of body length; while the control group was compared with gynogenetic group and increased for16.217%of body weight and13.18%of body length; single hybrids showed obvious advantages.This study firstly described the process of the gender differentiation and the gonadal development of the DH paralichthys olivaceus, which is of great significance for setting up the DH paralichthys olivaceus biology; And it was observed that there were more than35%of males in the DH paralichthys olivaceus for the first time, which is vital for studying the gender differentiation and changes of paralichthys olivaceus. By the gynogenesis hybrid of paralichthys olivaceus, it built the single cross hybrid of fish for the first time, and through the specific analysis of its growth and genetic aspects, it found that single cross hybrid of the paralichthys olivaceus possessed excellent heterosis and had a high genetic similarity, which means the method could be used as a new breeding way. The single cross hybrid established in this study has been examined and approved as excellent new species by the National Committee on Aquatic Product Quality. |
PDF Full Text Request