Abstract: Koi is a brightly coloured, elegant fish with high ornamental value, and is known as a “swimming work of art”. Fish body colour is mainly determined by the type and distribution of pigment cells on the skin or scales. In this paper, the composition, distribution and morphology of pigment cells in the scales and skin of four different body colours, namely, black, white, yellow and red koi, were compared. The composition of pigment cells in the scales and skin was consistent, and rich iridescent cells were present in all four koi, with melanophores in black koi, and xanthophores and erythrophores in yellow and red koi. Only iridophores were observed in white koi. The ultrastructure of iridophores in all four koi colours was observed by transmission microscopy, and the iridophores mainly had three different morphologies: pike-shaped, short rod-shaped and vacuolated. Real-time fluorescence quantitative PCR was used to detect the expression of eight iridocyte development-related genes in the skin of four different body colors of koi carp, the results showed that eight genes related to iridophores development were expressed in the skin of different body colours, whereas there were differences in expression, among which the relative expression of alk, pka, sox10, pax3, foxd3 and pnp4a genes was higher in red and yellow koi, while the relative expression of ltk and alx4a genes was the highest in white koi. In order to further confirm the role of the pnp4a genes in iridophores development, the recombinant plasmid of overexpression of pnp4a gene was constructed, and was microinjected into the fertilized eggs of AB zebrafish. In order to further confirm the role of pnp4a gene in fish body colour formation, especially in iridophores, we constructed a pnp4a overexpression recombinant plasmid and microinjected it into the fertilized eggs of zebrafish (AB).

Key words: koi; iridophores; pnp4a; body color development; gene expression

（Acta Laser Biology Sinica, 2024, 33(1): 031-039）