Phaeodactylum tricornutum in finishing diets for gilthead seabream: effects on skin pigmentation, sensory properties and nutritional value

Microalgal biomasses are known to play a major role in fish pigmentation, which is particularly important in farmed fish, since colour and external appearance are the first cue for customers when choosing seafood. A study was undertaken to assess the potential of microalgae biomass from the diatom Phaeodactylum tricornutum as a functional ingredient for gilthead seabream ( Sparus aurata ) feeds. Three experimental diets were designed: a control diet (CTRL), this same diet supplemented with 2.5% of P . tricornutum wild strain (diet MA20); and a third diet with 2.5% of P . tricornutum biomass (diet MA37) cultivated under different temperature and light regimes that resulted in higher levels of fucoxanthin. Microalgae diets led to a reduction ( P < 0.05 in MA37) of whole-body fat and lower lipid retention ( P < 0.05 in MA20 and MA37). Microalgae did not impact odour, flavour, whiteness, and fatness perception in cooked fillets. Overall, colour analysis showed that P . tricornutum biomass led to significant differences compared to control in specific areas: the MA37 diet induced a significantly ( P < 0.05) lighter and more vivid yellow colouration of seabream operculum (ΔE* ≈ 5) perceptible to the human eye; ventral skin lightness was also affected by the dietary treatments ( P = 0.040), being higher for microalgae-fed groups, though this difference was not perceptually strong (ΔE* ≈ 1.7). Phaeodactylum tricornutum biomass can be used as a functional ingredient, improving external pigmentation and thus contributing to meet consumer expectations in relation to farmed gilthead seabream.