Reduction of Anisakis Allergenicity in Gilthead Seabream (Sparus aurata) Fed with Fish Viscera Silage-Based Diets

Anisakis simplex allergens are highly resistant to conventional processing, posing a health risk that limits the use of infested fish both for human consumption and for animal feed. To assess the safety and nutritional value of viscera silage, hake (Merluccius merluccius) viscera were processed with formic acid and stored for four months. Two experimental diets were prepared—one containing silage and another with untreated viscera—alongside a commercial control feed. Juvenile gilthead seabreams (Sparus aurata) were fed these diets for 86 days, and growth performance, muscle composition, and allergenicity were analysed. All groups achieved more than 20% weight gain, and the silage-fed fish showed the lowest residual allergenicity (15.3%), compared to the fish fed untreated viscera (24%) and commercial feed (21.9%). Silage processing caused extensive protein hydrolysis, reducing high-molecular-weight proteins, though some IgE-reactive fragments remained. Proteomic analysis detected only seabream structural and metabolic proteins, with no confirmed Anisakis allergens. These findings indicate that silage produced from Anisakis-infested viscera should not pose a higher risk to consumers than the fishmeal used in aquaculture feeds and could support the valorisation of currently discarded fish viscera.