Comparative Analysis On Morphology, Growth And Genetic Structure In Grass Carp, Bighead Carp And Their F1 Hybrids

Grass carp( Ctenopharyngodon idellus),one of the famous"Four Major Chinese Carp", is an important economic fish in China ,even in the world ,with its largest production in freshwater fish species. However, in recent years, because of inbreeding, germplasm resources of grass carps seriously intermixed from different river systems , destruction of ecological environment, the genetic resources of grass carp degenerated ,such as it easily suffered from a variety of diseases in its cultivation. Therefore, the genetic improvement of grass carp is important for the conservation and utilization of genetic resources, and essential to sustainable development of the grass carp culture. As one of basic breeding means, distant hybridization has been made great progress in aquatic animal breeding. Bighead carp (Aristichthys nobilis) is one of compatible partners, because of low diseases and fast growing. In order to search for the approach of grass carp hybridization breeding, comparative analysis on growth, morphology and genetic structure in grass carp, bighead carp and their hybrids obtained by artificially cross of grass carp and bighead carp were made in this study. The results were briefly summarized as follows:1. Morphological variations in Ctenopharyngodon idellus ,Aristichthys nobilis and Ctenopharyngodon idellus♀×Aristichthys nobilis♂Three F1 progenies (C. idellus♀×C. idellus♂, A. nobilis♀×A. nobilis♂, C. idellus♀×A. nobilis♂) were obtained by artificial diallel cross of grass carp (Ctenopharyngodon idellus)and bighead carp(Aristichthys nobilis). Morphological variations among juveniles of grass carp, bighead carp and grass carp♀×bighead carp♂were analyzed by traditional morphometrics and the truss network analysis. As meristic characters, the numbers of dorsal fin spines, pectoral fin spines, pelvic fin spines were consistent in three F1 progenies. The statistical analysis of other meristic characters showed no significant differences between grass carp and grass carp♀×bighead carp♂in the numbers of dorsal fin rays and pectoral fin rays, but high significant differences between each of them with bighead carp, no significant differences among grass carp, bighead carp and grass carp♀×bighead carp♂in numbers of pectoral fin rays and pelvic fin rays, but high significant differences among lateral-line scales ,scale rows above and below lateral line were observed in three F1 progenies .The result of Cluster analysis and morphmetric parameters analysis based on the measurable character data and the truss network data of F1 progenies showed the grass carp♀×bighead carp♂F1 hybrids were closer to female parent grass carp in the aspect of morphology.2. Comparative analysis on growth in grass carp, bighead carp, grass carp♀×bighead carp♂at juvenile stageThe comparison test on growth of grass carp, bighead carp, grass carp♀×bighead carp♂at juvenile stage were analyzed by two cultivation models, first monoculture then polyculture in the net cage of pond. As 120 days'well cultivation, the result indicated: when cultured at 40th day ,there were no significant differences(P﹤0.05) between grass carp♀×bighead carp♂and bighead carp in body length, body weight, average individual daily weight gain(ADW), but high significant difference (P﹤0.01)existed between each of them and grass carp, and the order of ADW was grass carp♀×bighead carp♂﹥bighead carp﹥grass carp; at 120 th day the data analysis showed there were high significant differences in body length, body weight ,ADW and absolute growth rate among these three F1 progenies , compared with grass carp or grass carp♀×bighead carp♂, bighead carp kept good variety, also grass carp was superior to grass carp♀×bighead carp♂. At juvenile stage, the study indicated that at mononculture model of net cage in pond, the growth of grass carp♀×bighead carp♂existed a certain good varity ,but there was no heterosis in growth traits for grass carp♀×bighead carp♂at polyculture model.3. Molecular identification of Ctenopharyngodon idellus, Aristichthys nobilis and F1 progeny of their reciprocal hybridsReciprocal hybrids(C.idellus♀×A. nobilis♂, A. nobilis♀×C .idellus♂)were produced by inter-subfamily cross of grass carp (Ctenopharyngodon idellus) and bighead carp (Aristichthys nobilis) in this study. The genetic structure of 8 grass carp parents, 8 bighead carp parents, and their 92 F1 progenies was comparatively analyzed using microsatellite markers with 26 pairs of primers which there were 16 pairs of primers of grass crap and 10 pairs of primers from bighead carp. The results showed that no clear bands were detected in bighead carp parents only from one pair of primers(Ci06) of grass carp, no products were amplified in grass carp parents and gynogenetic individuals from three pairs primer(hljy1516,hljy2324,hljy3536) of bighead carp, and the remaining 22 pairs of primers could effectively amplify in all samples. However, with 13 specific-species loci screened out, specific bands showed combination of loci hljy1516 and loci Ci06 or other loci could effectively differentiate grass carp, bighead carp, F1 hybrids and gynogenetic individuals. Besides, mitochondrial control region (D-loop) sequence alignment between parental generation and hybrid generation was adopted to determine maternal origin of reciprocal hybrids based on the characteristics of maternal inheritance of mitochondria. Results demonstrated that combination of microsatellite markers and mitochondrial D-loop sequence alignment could well discriminate grass carp, bighead carp, their reciprocal hybrids and gynogenetic individuals.