Fish occupy a pivotal role as a premier source of high-quality animal protein, holding great promise for enhancing global dietary regimes. Despite their importance, a major limitation in about 70% of farmed fish species is the presence of intermuscular bones—a network of thin, needle-like bones embedded within the muscle tissue. These IBs not only pose risks during consumption, causing choking hazards and digestive challenges, but also limit the efficiency and application of modern fish processing technologies. Hence, breeding IB-free fish has long been identified as a paramount goal in aquatic genetic improvement programs.

The research team’s focus on the developmental biology and molecular regulation of IBs began over a decade ago, culminating in a pioneering elucidation of the genetic pathways underpinning IB formation in cyprinid fish. Central to these mechanisms is the runx2b gene, a pivotal transcription factor that orchestrates bone development, particularly influencing the ossification process of intermuscular bones. By employing the revolutionary CRISPR/Cas9 genome editing technique, the team precisely disrupted the runx2b gene in one-cell-stage grass carp embryos, generating targeted mutations in the F0 generation.

Subsequent breeding and genetic crossing of these F0 mutants yielded an F1 generation exhibiting heritable absence of IBs. Through rigorous phenotypic screening and selective mating, an F2 generation was established, conclusively demonstrating stable inheritance of the IB-free trait. This strategic molecular breeding pipeline not only bypasses the lengthy timelines and uncertainties of conventional selective breeding but also harnesses gene editing to produce novel, high-value germplasm resources rapidly.

Grass carp, the most extensively farmed fish species globally with projected production of 6.2 million tons in 2024, was chosen as the model for this study due to its widespread economic and nutritional significance. Traditionally burdened by approximately 118 intermuscular bones, these fish suffer from reduced consumer acceptability and processing challenges. The runx2b gene-edited grass carp revealed not only complete elimination of IBs but also exhibited normal development of the rest of the skeletal system, confirming that the editing was specifically targeted without detrimental off-target effects on major bone structures.

Comprehensive biochemical and nutritional analyses demonstrated that the absence of IBs did not alter the moisture, protein, lipid, amino acid, or fatty acid profiles in the muscle tissue when compared to wild-type control fish. Sensory qualities including free amino acid composition and flavor potential remained unaffected, indicating that meat quality was preserved post gene editing. Intriguingly, the IB-free fish displayed enhanced textural properties, with significantly increased gel strength, cohesiveness, and resilience—characteristics desirable for both consumer experience and industrial processing.

At the physiological level, the researchers observed a subtle shift in muscle composition, notably a decrease in calcium content and an increase in potassium concentration in the edited fish. These changes likely reflect adaptive mineral homeostatic mechanisms compensating for the absence of intermuscular skeletal supports. To investigate molecular alterations accompanying these physiological adaptations, the team conducted multi-omics analyses encompassing transcriptomics and metabolomics of muscle tissue.

Their molecular profiling revealed extensive remodeling of pathways integral to muscle function, particularly calcium signaling and muscle contraction pathways. Notably, genes associated with fast-twitch muscle fibers were upregulated, suggesting a phenotypic shift favoring enhanced contraction speed and metabolic efficiency. This remodeling is hypothesized to counterbalance the structural deficit caused by IB removal, enabling the fish to maintain normal locomotor performance and activity levels despite skeletal alterations.

Beyond scientific novelty, this study establishes a versatile and replicable technical framework integrating gene identification, precise genetic editing, controlled breeding, and rigorous safety and quality evaluations. Such a comprehensive system sets a new benchmark for aquatic genetic improvement endeavors, offering a blueprint for the development of fish strains with optimized traits tailored for modern aquaculture needs.

The broader implications of this research resonate across the global fish farming industry. By generating IB-free grass carp that retain nutritional and sensory attributes while enhancing processing performance, this innovation promises to elevate product safety, streamline industrial processing, and expand market potential. Moreover, it addresses consumer concerns over bone-related injuries and enhances the overall eating quality of farmed fish, supporting public health objectives related to protein intake.

This success derives from a collaborative effort between Huazhong Agricultural University—a leading institution in freshwater fish genetics and breeding—and Guangdong Haid Group Co., Ltd., a global agricultural technology enterprise dedicated to sustainable aquaculture development. Their combined expertise and resources effectively bridged fundamental research and practical application, accelerating the translation of gene editing techniques into viable commercial germplasm resources.

Looking forward, this breakthrough opens exciting avenues for genetic improvement of other aquaculture species. The universality of runx2b as a key regulatory target for IB formation suggests the potential for broad-spectrum application across multiple species with similar bone development pathways. Integration of such gene editing approaches with conventional breeding pipelines could revolutionize aquatic animal genetics, underpinning sustainable, efficient, and consumer-friendly fish production systems worldwide.

In conclusion, the generation of IB-free grass carp through runx2b gene editing marks a transformative milestone in aquaculture genetics. It addresses a long-standing industry challenge by harnessing cutting-edge molecular biology tools, while maintaining or improving key quality traits, ensuring fish welfare, and aligning with consumer demand for safer, more convenient seafood products. This pioneering research exemplifies how modern genetic technologies can foster innovation that benefits producers, consumers, and the environment alike, paving the way for the next generation of aquaculture excellence.

Subject of Research: Genetic editing of runx2b gene in grass carp to eliminate intermuscular bones

Article Title: Creation of Grass Carp Without Intermuscular Bones Through RUNX2B Gene Editing

Web References: DOI: 10.1007/s11427-025-3215-8

Image Credits: ©Science China Press

Keywords: Grass carp, intermuscular bones, runx2b gene, CRISPR/Cas9, gene editing, aquaculture genetics, skeletal development, muscle physiology, multi-omics analysis, sustainable aquaculture

Gold grass carp are highly valued for their striking golden coloration, which has made them popular in ornamental ponds and aquaculture ventures. However, these fish have been increasingly threatened by limited access to natural genetic materials and the adverse effects of prolonged inbreeding. As inbreeding continues, it leads to altered coloration in offspring, significantly higher deformity rates, and a decrease in the overall health of the population. The research team identified the tyrb gene as a crucial target that could potentially reverse these detrimental trends.

The methodology employed in this study involved microinjecting a carefully designed mixture of gRNA specific to the tyrb gene and the Cas9 protein into single-cell stage embryos. This innovative approach enabled the researchers to achieve efficient gene disruption. The targeted editing resulted in the production of red-eyed, golden mutants in the F0 generation, showcasing a dramatic reduction in the number of melanophores, which are responsible for dark pigmentation. As a consequence, the edited fish exhibited an impressive uniform coloration, characterized by a rich golden hue that is free from the irregularities that accompany traditional inbreeding practices.

What makes these red-eyed mutants particularly fascinating is their permanent alteration of color due to the irreversible loss of melanin in their ocular regions. Unlike their traditional black-eyed counterparts, which are prone to color deterioration over successive generations due to inbreeding, these genetically engineered mutants maintain a stable and attractive coloration. This stability positions them as a more viable option for ornamental fish farmers, providing an opportunity to meet consumer demand while ensuring the longevity of the species.

In addition to the aesthetic benefits, the increased genetic robustness observed in the red-eyed mutants hints at a promising future for the aquaculture industry. The mutated grass carp not only demonstrate enhanced ornamental qualities but also show greater resilience against diseases, a critical factor in fish farming operations. By mitigating the risks associated with inbreeding, the research presents a viable framework for sustaining and enhancing the quality of ornamental and edible fish species.

Moreover, the innovative use of multiple gRNAs in the CRISPR/Cas9 process indicated a remarkable increase in mutation efficiency and large-scale deletions of unwanted genetic material. This methodological breakthrough provides a replicable technical framework for gene editing not only in grass carp but potentially in other fish species as well. The implications of this breakthrough extend beyond just the immediate results; they could fundamentally reshape breeding practices across various aquaculture settings, accommodating demands for both high-value ornamental varieties and improved food sources.

Interestingly, the research also addressed earlier concerns tied to the use of gene-editing technologies, particularly regarding their effects on the overall survival and development of the modified organisms. The team observed that the knockout of the tyrb gene selectively influenced pigmentation without leading to developmental defects in the grass carp. This suggests that the tyrb gene plays a distinct role primarily in processes involving pigmentation rather than essential growth and development, allowing for targeted edits without unintended consequences.

As such, the findings represent a significant advancement in the field of molecular-designed breeding. The stability of the golden germplasm developed through this research could very well herald a new era in aquaculture practices. This approach not only addresses some of the pressing challenges currently faced by traditional fish breeding but also encourages the advancement of high-value ornamental and food fish varieties that can appeal to diverse markets.

Future research building on these findings could enhance the efficiency of gene editing techniques even further, potentially widening the scope of species that could benefit from CRISPR/Cas9 interventions. Tackling genetic concerns effectively opens up a wealth of possibilities for aquaculture sustainability, industry growth, and the preservation of biodiversity. As researchers continue to explore the genetic underpinnings of aquaculture species, it is anticipated that similar approaches will lead to the development of breakthrough solutions for various challenges faced by the industry.

In conclusion, the successful disruption of the tyrb gene in grass carp underscores the revolutionary potential of CRISPR technology in aquaculture. The research showcases how strategic genetic modifications can overcome the pressing challenges of inbreeding, enhance coloration, and improve the overall health of cultured species. As the industry looks toward a future informed by these advances, it is clear that research like this will play a crucial role in shaping sustainable aquaculture practices for generations to come.

Subject of Research: Animals
Article Title: Highly efficient disruption of tyrb gene using CRISPR/Cas9 in grass carp (Ctenopharyngodon idella)
News Publication Date: October 2023
Web References: KeAi
References: Available upon request
Image Credits: Credit: Xingyong Liu, et al.

Keywords: Aquaculture, CRISPR/Cas9, Grass Carp, Genetic Editing, Ornamental Fish.