Analysis of differences in body color characteristics between wild and hatchery-reared juvenile marbled rockfish (Sebastiscus marmoratus)

Significant differences in body coloration exist between hatchery-reared and wild fish. These differences not only affect the ornamental and economic value of the fish, but may also reflect variations in their physiological status and environmental adaptability. To clarify the differences in body coloration characteristics and the underlying mechanisms between hatchery-reared juvenile marbled rockfish (Sebastiscus marmoratus) and their wild conspecifics, we employed in situ visual quantitative analysis, colorimetric measurements, and histological analysis to systematically compare the skin color patterns, colorimetric parameters, spatial distribution patterns of pigments, and skin pigment mass concentrations between the two groups. The results show that: 1) There were significant differences in the distribution of melanin spots on the body surface between wild and hatchery-reared S. marmoratus. The melanin spots of wild individuals were regularly distributed and concentrated on the dorsal part of the body, whereas those of hatchery-reared individuals were relatively scattered. 2) The skin lightness (L^*) and redness (a^*) values of wild S. marmoratus were extremely significantly higher than those of hatchery-reared individuals (p<0.001). Additionally, the wild individuals exhibited higher overall skin chromaticity, resulting in a large color difference (∆E>4.0) compared with hatchery-reared individuals. 3) Significant differences were observed in the morphology, size, and distribution of skin pigment cells between the two groups. The skin pigment cells of wild individuals were mostly small and granular, with an extremely significantly higher distribution density than those of hatchery-reared individuals (p<0.001). In contrast, the pigment cells of hatchery-reared individuals were mostly dendritic, and their cell area was extremely significantly larger than that of wild individuals (p<0.001). 4) The skin pigment mass concentrations of wild S. marmoratus were significantly higher than those of hatchery-reared individuals (p<0.05). In conclusion, the significant differences in the composition and distribution of skin pigment cells, as well as skin pigment mass concentrations, between wild and hatchery-reared S. marmoratus are important factors leading to the distinct external body coloration characteristics between the two groups.