An innovative colorimetric calibration method used to quantify differences among wild and reared gilthead seabream (Sparus aurata, Linnaeus 1758)

The appearance of a product is a primary criterion in the purchasing decisions of consumers, being at the base of selection judgement of the product’s individual units quality. Appearance characters are defined by size, shape, form, colour and absence of visual defects. Appearance is utilized as a selection criterion throughout the market production chain, storage, marketing, and finally the utilization. Fish experts affirm to be able to visually discriminate among wild and reared fish of the same species by the fish colours. For the European fish market gilthead seabream (Sparus aurata) is, together with seabass (Dicentrarchus labrax), the most important marine cultured species. A novel colour calibration method based on the association between a standard colour chart and a Partial Least Squares (PLS) model developed in Matlab environment was developed. RGB declared values of the ColorCheker (24 patches) were used as y-block. The x-block was represented by the mean RGB values of the same 24 patches. Once colorimetrically calibrated, the images of 20 wild and reared seabreams were shape adjusted with landmark based geometric morphometric tools. Superimposed fishes were then compared with a PLS Discriminant Analysis. The results quantified differences between wild and reared fish. The proposed method of colour calibration allows the automatic finding out of frauds (reared fish sold as wild ones) and the identification of rearing methodologies able to produce wild-like gilthead seabream, in addition to quantitative investigation of other food products reducing the colour variance due to external factors.