Lack of intermuscular bones in specimens of Colossoma macropomum: an unusual phenotype to be incorporated into genetic improvement programs

Colossoma macropomum , commonly known as tambaqui, is the second largest scaled fish in South America and is mostly distributed in Amazon river systems. This fish is the first native species used in fish farming in Brazil. Intermuscular bones are regarded as ossified tendons or spicule-like bones inserted into the myosepta of the fillet of teleost fish. These bones are present in ostariophysi fish, such as Cypriniformes and Characiformes, and representatives of these two orders include important aquaculture species. In this study we describe the absence of intermuscular bone among broodstock C. macropomum in a fish hatchery located in northwestern Brazil. Tambaqui breeders from which the boneless tambaqui were thought to have originated were assessed by X-ray. We then used ultrasound as a new methodology for imaging intermuscular bones. Twenty-eight out of 120 broodstock were identified as either lacking intermuscular bones or having vestiges of these bones. This finding may provide the basis for important research aimed at understanding the genetic origin of this phenotype, which could then be incorporated into genetic breeding programs to develop other boneless strains of tambaqui as well as other Characiforme and Cypriniforme species. Statement of relevance The present study describes for the first time Colossoma macopomum (tambaqui) adult individuals lacking intermuscular bones, an important trait for aquaculture fish species.