Electronic eye to evaluate skin pigmentation of Sparus aurata fed with different level of Hermetia illucens meal.

Limited information exists on the effects on quality traits of cultured fish fed insect meal as a partial substitute for fish meal (FM). Fish skin pigmentation is one of the most important quality criteria dictating the market value of fish for human consumption. Aim of this study was to assess the pattern of color pigmentation of the skin in Sparus aurata fed four diets isoenergetic (22 MJ/kg gross energy), isonitrogenous (43 g/100g, as fed) and isolipidic (19 g/100 g, as fed) containing 0%, 25%, 35% and 50% of Hermetia illucens meal (HIM) in substitution of FM. The fish (324) were divided into 4 groups: FM, HI25, HI35 and HI50 corresponding to the inclusion levels of 0%, 7.9%, 11% and 15.7% of HIM, respectively. At the end of the trial, 18 fish per diet were sacrificed and photographed both in the left and the right side in a measurement chamber, with a camera for high-resolution data acquisition (16 million colors) by using an electronic eye (Iris Visual Analyzer 400-Alpha MOS). RGB code for each color extracted from the different images was obtained, and used as input for the statistical analysis. Exploratory data analysis was performed with principal component analysis (PCA) and expressed based upon the discrimination index (DI). Then, 7 colors with higher discrimination power were selected, a discriminant function analysis (DFA) was performed and validation score (VS) expressed. On the basis of Mahalanobis distance, the pattern discrimination index (PDI) among the 4 groups was calculated. PCA discrimination explained 84.63% of the variance but showing a negative DI (313). DFA analysis with the 7 best-performing sensors had a positive VS (48), but not sufficient to distinguish the 4 groups. Also the PDI were very low showing minimal difference for skin pigmentation between conventional FM group and HI25, HI35 and HI50 (6.32%, 6.33% and 3.05% respectively). Results, through an automatic image analysis tool, showed that inclusion of H. illucens in aquafeed had low impact on skin pigmentation of S. aurata, making this ingredient as a potential sustainable protein source for as animal feed.