Fish serve as a vital source of high-quality animal protein and play a crucial role in improving global dietary patterns. However, approximately 70% of farmed fish worldwide possess intermuscular bones (IBs), which not only compromise eating safety but also restrict modern processing, presenting a major bottleneck for industry advancement. Breeding IB-free fish has therefore become a key objective in global aquatic animal genetic breeding.
To address this challenge, a research team led by Prof. Gao Zexia from Huazhong Agricultural University has been working since 2012 on the developmental mechanisms and genetic improvement of fish IBs. The team was the first internationally to elucidate the developmental and ossification processes of IBs, identify the key regulatory gene runx2b responsible for IB formation, and establish a molecular precision breeding system for IB-free fish.
Grass carp is the most produced farmed fish globally, with an output of 6.2 million tons in 2024. It is valued for its mature culture technology, high nutritional value and environmental friendliness. Yet, like most cyprinids, grass carp carries about 118 IBs, which severely limit its market potential. In this study, while revealing the complex morphology and critical ossification period of IBs in grass carp, the researchers utilized runx2b gene editing to successfully create a novel, stably inheritable grass carp germplasm without IBs.
Addressing the core concern of whether “IB-free” fish retain their quality, the study confirmed that the absence of IBs did not affect the development or mineralization of other major skeletal structures, nor did it alter overall body composition. Nutritionally, IB-free and wild-type grass carp showed no significant differences in moisture, protein, fat, amino acid or fatty acid profiles, and their free amino acid composition and flavor potential were comparable. However, the IB-free carp exhibited significantly higher gel strength, cohesiveness, and resilience, along with a slightly lighter muscle color. A reduction in muscle calcium and an increase in potassium were also observed, possibly reflecting physiological adaptation in mineral balance.
Multi-omics analysis further revealed a systemic molecular remodeling in the muscle of IB-free carp: significant changes in Calcium Signaling and Muscle Contraction pathways, coupled with changes of genes associated with fast twitch fibers, suggest a possible enhancement of fast muscle fiber types in IB-free grass carp and the fish enhance oxidative metabolism and contraction efficiency to physiologically compensate for the lack of skeletal support, thereby maintaining normal motor performance.
This study not only validated the universality of runx2b as a key target for the genetic improvement of IBs in fish, but also provided a comprehensive technical framework encompassing gene identification, genetic editing breeding, as well as safety and quality assessment. It offers theoretical and technical references for breeding high-value, easily processed new aquatic varieties.
This study was completed in collaboration between Huazhong Agricultural University and Guangdong Haid Group Co., Ltd. Huazhong Agricultural University has a long history in aquaculture disciplines and possesses a solid foundation in the field of freshwater fish genetics and breeding. Guangdong Haid Group is a global agricultural technology enterprise whose business covers the entire industry chain, including feed, seedlings, animal health, and food processing. The company is committed to driving the sustainable development of aquaculture through technological innovation.
Science China Life Sciences
Experimental study