# Body Coloration Characterization and Proteomic Analysis of Diurnal Color Variation in Farmed Larimichthys crocea

## TL;DR

This study explores the golden coloration and daily color changes in farmed large yellow croaker, identifying pigments and proteins involved in color variation.

## Contribution

The study reveals the role of xanthophores and motor proteins in diurnal color changes and links carotenoid content to skin yellowness in large yellow croaker.

## Key findings

- Xanthophores containing lutein are most abundant in ventral and caudal skin, contributing to the fish's golden color.
- Diurnal color variation is driven by the movement of xanthosomes within xanthophores, likely controlled by motor proteins like KIF21 and DYNC1L1.
- Skin yellowness strongly correlates with total carotenoid content (R = 0.91, p < 0.05), with lutein esters being the main contributors.

## Abstract

The golden color of the farmed large yellow croaker is highly prized by consumers, directly affecting its market price. This study investigated what gives this fish its yellow coloration and why its color can change between day and night. We found that special yellow pigment cells (xanthophores), containing pigment granules called carotenoids (mainly lutein), are most abundant in its ventral and caudal skin. The fish’s diurnal color change is driven by the movement of these yellow pigments granules (xanthosomes) within the cells, likely controlled by specific motor proteins. This research helps us understand the biology behind the fish’s coloration. The findings provide a scientific basis for aquaculture breeders to improve the desirable golden color in this important seafood species through selective breeding or feed, ultimately delivering a better product to the market.

The large yellow croaker (Larimichthys crocea) is an economically significant aquaculture species in Asia, with skin coloration being a key quality attribute affecting consumer choice and commercial value. This study integrated morphological, biochemical, and proteomic approaches to investigate chromatophore characteristics, pigment composition, and diurnal body color variation in the large yellow croaker. Colorimetric analysis showed the highest yellowness, redness, and lightness values in ventral skin, followed by caudal skin, with dorsal skin showing the least yellowness. Three major chromatophores were identified: melanophores, xanthophores, and iridophores. Xanthophores were abundant in ventral and caudal skin, showing larger size and deeper pigmentation ventrally, while melanophores dominated dorsally and iridophores were mainly on scales. Skin and fins were key sites for carotenoid deposition, with lutein as the predominant carotenoid. Esters of lutein and zeaxanthin were the main contributors to yellow coloration in fish. A strong positive correlation was found between skin yellowness and total carotenoid content (R = 0.91, p < 0.05). The aggregation and dispersion of xanthosomes within xanthophores appeared to be the key driver behind the light-influenced diurnal body color variation. Proteomic analysis revealed motor proteins (such as KIF21, DYNC1L1, and MYO9) and pathways related to intracellular granule movement were probably related to the pigment transport in chromatophores of large yellow croaker. In addition, tubulin dynamics also appeared to participate in pigment translocation. This study is helpful to understand the pigmentary basis of this important farmed sea fish and provides a foundation for improving the golden color traits and further molecular research on diurnal color changes in large yellow croaker.