Understanding the development of intermuscular bones in teleost: status and future directions for aquaculture

As one of the most sustainable protein sources for humans, aquaculture is the fastest growing food production sector in agriculture. According to the recent FAO estimate, there are 21 principal aquaculture fish species around the worldwide. Among these cultured species, almost half of them belong to Cypriniformes, the species from which all have a certain number of intermuscular bones (IBs). IBs are small spicule-like bones existing in the muscle fillet, which are existed only in lower teleost and of course have a negative effect on fish quality and aquatic product processing. Many studies have been focusing on IBs number, morphology, and more and more become focusing on its development molecular mechanism. In the review, we summarized the recent progress and discussed with following directions: (i) Controversial on the origin of IBs, ossified from tendons or ligaments? (ii) IBs counts and morphology revealed big variation among different species; (iii) Ossification patterns of IBs might be related with different swimming modes among the teleost fish, and its development belongs to intramembranous ossification without cartilaginous phase; (iv) Transcriptome/microRNA (miRNA)/proteomics and gene functional analysis had been used to investigate the molecular mechanism of IBs development and some genes showed certain regulatory roles during IBs' development; (v) The reports showed that some breeding technologies could make a certain effect on IBs counts in fish species, but there are rare reports with success on deleting or significantly reducing IBs counts. Meanwhile, we also discuss the challenges and future directions of reducing or even deleting IBs in aquaculture.