Sea bream fillet quality as affected by alternative protein sources in diet

Gilthead seabream (Sparus aurata) has been the object of intensive farming as early as the seventies. Nowadays it represents the most popular marine finfish in Italy and its farming is an important activity both for the productive volumes and economical value. As part of the aquaculture sector, seabream farm is suffering for feedstuff shortage, being fishmeal and oil highly unsustainable. Thus, the present study aimed to evaluate different protein sources in seabream diet: (i) a fish meal-based (54%) control diet (CF), (ii) a plant protein meal-based control diet (CV); the other four diets were based on the CV diet, with: (iii) 10% substitution with a mixture of microalgae (Tisochrysis lutea and Tetraselmis suecica) meal (M10), (iv) 10% substitution with the meal obtained by processing the invasive alien Louisiana red swamp crayfish (Procambarus clarkii) (R10), (v) 20% substitution with poultry by-product meal (PBM) (P20), (vi) 40% substitution with insect meal (Hermetia illucens) (H40). Ten fish per group were sampled at the end of the growing trial and the physico- chemical characterization of fish fillets was assessed. The results revealed that M10 diet slightly but significantly decreased fish total body weight (around 303 g against 335 g, as average of the other groups). Despite this, M10 fish had analogous fillet yield than the other groups (53%). Diets differently affected skin and fillet color values. Specifically, the results of skin color indexes (lightness, L*; redness, a*; yellowness, b*) displayed differences in the skin of the fish fed with M10, which was significantly lighter than the P20 group skin (L*: 76.41 and 69.69, respectively). Fish fed H40 showed a b* index (1.28) significantly higher than the b* value of CF group (−3.85). Contrariwise, fillet color values were not modified by the dietary treatments. Looking at the nutritional values, the incidence of polyunsaturated fatty acid (FA) of the n-3 series was higher in CF fillets (23.86 g/100 g total FA) than in the other groups (19.51 g/100 g total FA, as average), while M10 and CV fillets had interesting amount of C18:3n-3 (8.37 and 8.46 g/100 g total FA, respectively). To sum up, microalgae seemed to induce the major changes in fish characteristics, while all the other ingredients could be considered to replace conventional protein sources in aquafeed for gilthead seabream. Acknowledgements Authors acknowledge SUSHIN (SUstainable fiSH feeds INnovative ingredients) Project funded by AGER 2-SUSHIN, Cod 2016–0112.