Avenues of genome editing for color trait improvement in ornamental fishes: current status and future perspectives.

Ornamental fish industries are growing sectors contributing significantly to livelihood, trade and export, driven by the worldwide demand for colourful and unique species. Pigmentation is the focal point of the visual appeal of ornamental fish, market value, and species-specific interaction. The pigment cells are called chromatophores, derived from neural crest cells and controlled by sophisticated genetic mechanisms, conferring these fish with distinctive colours and patterns. Historically, selective breeding and dietary pigment supplementation have been applied to enhance colouration. Such traditional practices, however, are prone to disadvantages such as slow development, genetic ambiguity, and unforeseen consequences. With the invention of genome editing, such as CRISPR-Cas9, researchers now have a sensitive and powerful tool to control pigmentation traits at the genetic level. Central pigmentation gene manipulation, such as Tyr, Mc1r, and Slc45a2, can allow researchers to introduce stable and uniform color changes. Such enhancements confer unparalleled control of fish colour, a promising avenue in the ornamental fish industry. This review discusses the genetic nature of fish pigmentation. It reports recent advances in CRISPR-based modifications and describes their possible applications and implications for future ornamental fish breeding.