| Hybridization is the most commonly used way in fishes breeding. Taking Platichthys stellatus, Kareius bicoloratus and their reciprocal hybrids as the research object, their traits variations were discussed from four aspects, such as embryonic development, morphological characteristics, growth performance, nutritive composition of muscle, and chromosome karyotype. The trials were conducted at Kehe ocean high-technologies company of Shandong, China. Results of the study are presented as follows: Experiment 1: The observation on the embryonic development of the reciprocal hybrids between Platichthys stellatus and Kareius bicoloratusThis paper presents the results of the research on the embryonic development of the reciprocal hybrids between P. stellatus and K. bicoloratus by means of artificial wet insemination. The fertilized eggs of the reciprocal hybrids between P. stellatus and K. bicoloratus were of separate sphericities without little oil ball, they were floated in sea water. The mean sizes of the fertilized eggs of the obverse hybrid(P. stellatus♀×K. bicoloratus♂) were 1.14-1.25 mm in diameter, and the mean sizes of the fertilized eggs of the inverse hybrid(K. bicoloratus♀×P. stellatus♂) were 1.09-1.16 mm in diameter. The embryonic development of the reciprocal hybrids between P. stellatus and K. bicoloratus passed through some phases: cleavage stage, blastula stage, gastrulae stage, neurula stage, blastopore closed, formation of optic vesicle and somite, tail-bud formation, crystal formation, otocyst formation, pre-hatching stage, hatching stage. And this paper provides the developmental characteristics of these phases. In 9-10℃ sea water, the larvae of the obverse hybrid hatched out at about 126 h after fertilization, and the total length of the newly hatched larvae was 2.90-3.12 mm, the long diameter of yolk sac was 1.57-1.83 mm and short diameter was 0.80-0.87 mm. In 9-10℃ sea water, the larvae of the inverse hybrid hatched out at about 134 h after fertilization, and the total length of the newly hatched larvae was 2.85-3.09 mm, the long diameter of yolk sac was 1.45-1.66 mm and short diameter was 0.71-0.78 mm. Experiment 2: Morphological variations and growth performances analysis of the reciprocal hybrids between Platichthys stellatus and Kareius bicoloratusMorphological variations and growth performances of P. stellatus, K. bicoloratus and their reciprocal hybrids were measured and analyzed. The results showed that the ratios of left eye type in obverse hybrid and inverse hybrid were 66.9% and 57.3%, which was between P. stellatus(84.7%) and K. bicoloratus(0%); in the reciprocal hybrids, similar scales with P. stellatus distributed on the equivalent body position where bone plates occurred in K. bicoloratus; and they had similar stripes with P. stellatus on their dorsal fin, anal fin and caudal fin, but they were smaller and more light colored; furthermore, the lateral lines of the obverse hybrid and P. stellatus bent at the end of the pectoral fin, however, the lateral lines of the inverse hybrid and K. bicoloratus were approximately linear. The average hybrid index of meristic characters of the two hybrids were 20.73 and 20.76, indicating their meristic characters inclined to their female parents, the same as the results of the chi-square analysis. Among eleven metric character ratios, more metric characters were not significantly different(P>0.05) between the hybrids and their female parents, and the average hybrid index of the two hybrids were 27.16 and 26.47, indicating their metric characters inclined to their female parents, the same as the results of the cluster analysis. Four discriminant functions were established in discriminatory analysis, the average discriminant accuracy was 97.50%, the discriminant effect was very ideal. In principle component analysis, four principal components were constructed by factor loadings and the cumulative contributive proportion was 82.562%, scatter plots showed that the morphological differences of the two hybrids were independent from P. stellatus and K. bicoloratus. The growth performances of the four fishes were not significantly different. Therefore, multivariate analysis on meristic characters and metric characters could be feasible to identify and distinguish the morphological variations among P. stellatus, K. bicoloratus, and their reciprocal hybrids. The study indicated that the reciprocal hybrids between P. stellatus and K. bicoloratus resembled P. stellatus in eye position, scale and fin morphological characteristics, and resembled their female parents in lateral line, meristic characters and metric characters. The study would be beneficial for P. stellatus, K. bicoloratus and their reciprocal hybrids to discriminate morphological characteristics, determine genetic relationships, and breed excellent hybrids. Experiment 3: Analysis and evaluation of nutritional composition in muscles of Platichthys stellatus, Kareius bicoloratus and their reciprocal hybridsReciprocal hybrids of P. stellatus and K. bicoloratus have been reported, however, little is known about the nutritional facts of their muscles. In this study we analyzed the nutritional components in muscles of P. stellatus, K. bicoloratus and the reciprocal hybrids(initial body weight 338.32–445.98 g) using the current national standard methods. We found that the obverse hybrid had significantly higher crude protein content than the inverse hybrid(P<0.05), but not significantly different from that of P. stellatus and K. bicoloratus(P>0.05). The crude lipid content of the obverse hybrid(1.44%) was significantly higher than that of the other three species(P<0.05). The inverse hybrid had the lowest level of crude lipid(0.43%) and significantly higher moisture level than the other three species. There was no significant difference in the muscle ash content among the four species(P>0.05). The obverse hybrid had significantly lower juice loss yield, water loss yield and fat loss yield than P. stellatus and K. bicoloratus(P<0.05), and its cooked meat yield was obviously higher than that of the inverse hybrid(P<0.05). The obverse hybrid possessed the highest contents of essential amino acid, delicious amino acid and total amino acid, and its ratio of branched-chain amino acid amount to aromatic amino acid amount was close to the normal value in humans. The contents of essential amino acids in the four species were higher than the Food and Agriculture Organization of the United Nations/World Health Organization(FAO/WHO) standard, moreover, it was the highest in the obverse hybrid of which the level was even higher than egg protein standard. The obverse hybrid had remarkably higher amino acids score(AAS), chemical score(CS) and essential amino acid index(EAAI) than the other three species, whereas the inverse hybrid had the lowest scores. These findings indicated that the obverse hybrid showed apparent hybrid advantages and exhibited higher nutritional values and muscle qualities than P. stellatus and K. bicoloratus. However these advantages were not present in the inverse hybrid. Our study provided valuable information for the selection of traits in the breeding between P. stellatus and K. bicoloratus. Experiment 4: Analysis of chromosome karyotypes of the reciprocal hybrids between Platichthys stellatus and Kareius bicoloratusThe karyotypes of the reciprocal hybrids between P. stellatus and K. bicoloratus were studied through the chromosome preparations obtained from head kidney by the method of injecting PHA and colchicine. After low permeating and Carnoy’s fixation, air drying method was used to make chromosome samples, which were dyed by Giemsa afterwards. The karyotypes were analyzed. The results showed that the chromosome numbers of the reciprocal hybrids between P. stellatus and K. bicoloratus were all 2n=48, including 47 telocentric chromosomes and 1 sub-middle chromosomes and there was no visible evidence of polyploidy chromosome, heterotypical sex chromosome and satellites. The karyotype formula was 2n=48=1sm+47t, NF=49. |
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