Formation of asymmetric body color in the caudal fin of common carp (Cyprinus carpio)

Abstract

Color pattern is one of the most important characteristics of species, which plays essential roles in reproduction, adaptability, and even survival. The adult caudal fin of common carp (Cyprinus carpio) has an asymmetrical distribution of body color, with the dorsal lobe (DL) being dark-gray and the ventral lobe (VL) being red. This study first investigates the cytological basis of forming such an asymmetric distribution by observing the component of pigment cells and exploring the early development of the body color, combined with adult caudal fin regeneration experiments in the common carp. In terms of the distribution feature and the number of pigment cells, differences between the DL and the VL are demonstrated, especially with respect to their erythrophores. Abundant lipid droplets and carotenoid droplets are observed in the VL, conforming to the distribution of erythrophores. Analysis of the gene expression profiles indicates that there are highly expressed levels of carotenoid deposition and lipid droplets transport genes, such as scarb and plin6. In contrast, the gene expression levels of the β-carotene dioxygenase (bco) family are significantly down-regulated in the VL. In addition, knocking down of the bco2a gene expression level causes a significant increment of erythrophores. It is concluded that the directed accumulation of lipid droplets and carotenoid particles is the reason for the asymmetric distribution of red color in the caudal fin of common carp.