A method for the comparison of chromaticity parameters in fish skin: Preliminary results for coloration pattern of red skin Sparidae

Skin coloration patterns in fish are of great physiological, behavioural and ecological importance, can be considered as an index of animal welfare in aquaculture and as an important quality factor for the retail value, especially of red skinned fish. In the present study we developed an appropriate method for comparisons of the skin chromaticity parameters in wild (Pagrus pagrus, Pagrus caeruleostictus, and Dentex gibbosus) and farmed red skin Sparidae and investigated the effect of storage time on skin colour of farmed Pagrus pagrus. The three-dimensional characteristics of colour appearance (lightness — L⁎, hue — H°ab and chroma —Cab⁎) were calculated. A new index, named Entire Colour Index (ECI), was developed to express hue and chroma which as combined variables, cannot be considered separately. In all species there was a remarkable dorsoventral gradient in mean L⁎ and H°ab, with the ventral area being statistically significant brighter than the dorsal one. ECI value was species specific but did not show any statistically significant dorsoventral gradient, with the exception of P. pagrus. Skin melanin and carotenoids content presented differences between the Pagrus and the Dentex species that may explain the differences in the observed chromaticity pattern. Storage time affected lightness and hue only in the dorsal skin area. However, the effect of storage on ice was better reflected in mean ECI value which showed a marked decrease from Day 3 to Day 7 in both the dorsal (Day 0: 8.96 ± 0.40; Day 7: 2.86 ± 0.29) and ventral (Day 0: 8.97 ± 0.18; Day 7: 4.10 ± 0.29) skin area. Our results provide data for a non-subjective determination of skin colour pattern and show that ECI offers a good index of the actual colour in a meaningful and objective way.