Genetic parameter estimates for intermuscular bone trait in grass carp (Ctenopharyngodon idella)

Intermuscular bones (IBs) are ossified myoseptal tendons, occurring only in teleosts among recent vertebrates. Most aquaculture species in the world contain a certain number of IBs, especially cyprinid fishes. The large number of IBs that are not easy to separate have seriously affected the edible and processability of fish and reduced the economic value of freshwater cultured fish. Grass carp (Ctenopharyngodon idella) is one of the major aquaculture species in the world with the certain number of IBs. In order to explore the possibility of reducing the number of IBs in C. idella by selective breeding, the genetic parameters for IBs trait of C. idella were evaluated in this study. The high polymorphic microsatellite loci were used to genotype 136 parents (66 males and 70 females) and their 538 offspring from cross breeding. After counting the IBs number and estimating the genetic parameters, animal models were used to evaluate the heritability of tested traits. The results showed that the IBs number of whole fish body was ranged from 102 to 127 with the average of 117, coefficient of variation (CV) being 3.23%. The CV of epipleural bones number in the ventral section (5.53%) was significantly higher than that of epineural bones in the dorsal section (2.52%). The heritability of IBs number in C. idella showed low level (0.137) for whole body, and epipleural bones had the lower heritability (0.068) compared to that of epinleural bones (0.132), which indicated the difficulty of traditional selective breeding for reducing IBs. However, the results found a high and significant genetic correlation between body height and whole body IBs number (0.918, p < 0.05), especially between body height and ventral IBs number, which may provide a new reference index for future breeding research on IBs number trait. The study reported the genetic parameters of IBs trait in C. idella for the first time, the low level heritability, but high genetic correlation between body height and IBs number, providing a reference of family-based breeding to obtain grass carp with less IBs.