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Megalobrama amblycephala, which belongs to the genus Megalobrama of the subfamily Culterinae in the family Cyprinidae, is an important freshwater cultured species in China because of its low culture cost and high growth rate. Culter alburnus, belonging to the subfamily Culter, is another slender carnivorous species, whose meat is more delicate and delicious than that of M. amblycephala; however, the scales of C. alburnus are small and thin and are easily injured and fall off, and these fish are slow-growing and expensive to feed. Although both the fish are quite different in terms of diet, growth, and stress resistance, they are highly complementary to each other. Crossbreeding can combine the desired characteristics of both parents; however, this advantage is usually limited to the F1 generation. Theoretically, because the gonads are almost undeveloped during triploid growth and development, F1 heterosis can be maintained to avoid germplasm decline caused by continuous reproduction, and energy can be saved to accelerate growth and improve muscle quality. This will greatly expand the breeding space of new hybrid varieties and ensure high economic, social, and ecological value. Therefore, the triploids of M. amblycephala ♀ × C. alburnus ♂ have superior growth and economic value. To understand the growth and morphological characteristics of the triploids of M. amblycephala ♀ × C. alburnus ♂, the triploid population of M. amblycephala ♀ × C. alburnu ♂ was induced by hydrostatic pressure, and successfully induced triploid (hybrid-3n) and uninduced diploid (hybrid-2n) populations were obtained. At the same time, two self-breeding populations of Megalobrama (MA) and Culter (CA) were established. The growth performance and morphological characteristics of the four kinds of fish were compared and analyzed in growth contrast experiments. The results showed that during the 210-day growth cycle, the absolute weight gain (0.88±0.11 g/day) of hybrid-3n was 8.64% higher than that of hybrid-2n, 20.55% higher than that of MA, and 120.00% higher than that of CA. In terms of countable traits, the hybrid index of hybrid-3n and hybrid-2n was 41.05 and 36.07, respectively. In terms of measurable traits, the hybrid index of hybrid-3n and hybrid-2n was 36.73 and 57.57, respectively. Cluster analysis showed that hybrid-3n was first grouped with hybrid-2n, then grouped with maternal MA, and finally grouped with paternal CA. The results showed that hybrid-3n and hybrid-2n were closer to their mothers in quantifiable traits and frame structure, showing a maternal effect. Discriminant analysis showed that the discriminant accuracy of hybrid-3n was 90%, and the comprehensive discriminant rate of the four populations was 95%. A scatterplot of the discriminant analysis showed that the distribution centers of hybrid-3n and hybrid-2n were located between the parents and closer to the mothers. Hybrid-3n and hybrid-2n occupied partially overlapping areas, which indicates that the two are similar in proportion and frame structure, making it difficult to distinguish between them. These results are basically consistent with those obtained by cluster analysis. Most of the 11 biological traits used to construct the discriminant function were related to the longitudinal axis of the body, especially the ratio of the height of the body to the trunk, which is similar to the results obtained by principal component analysis. During principal component analysis, four principal components with a cumulative contribution rate of 75.10% were obtained, which mainly reflect morphological variations of body height and trunk length. In this study, the experimental fish were cultured in still water ponds with abundant bait. The morphological differences may be attributed to the adaptation of the fish to this ecological environment. Comprehensive analysis showed that: Hybrid-3n has a fast growth rate and has the basic conditions for promotion and application in production; The body size of hybrid-3n and hybrid-2n is between the parents, and both are slightly biased towards the mother, which mainly reflect the morphological variations of body height and trunk length; In this study, three multivariate analyses were used to effectively reflect the morphological differences among the four populations of hybrid-3n, hybrid-2n, MA, and CA from different perspectives, which has made them irreplaceable. In conclusion, this study confirmed the superior breeding potential of triploids of M. amblycephala ♀ × C. alburnu ♂, and provided basic data for the morphological comparison of hybrid offspring of M. amblycephala and C. alburnu, which is significant for the identification and protection of fish resources, and is expected to provide a theoretical basis for the establishment of new strains of M. amblycephala and C. alburnu. The results are of great significance for population identification and ploidy breeding of hybrid offspring of M. amblycephala and C. alburnu. |
