Comparative Effects of Untreated and High-Solid Loading Pre-Treated Codium tomentosum on Oxidative and Immune Responses in European Seabass (Dicentrarchus labrax)

Abstract

The effects of dietary inclusion of the macroalgae Codium tomentosum, either untreated or pre-treated with high-solid-loading alkaline hydrolysis, on the oxidative status, intestinal immune responses, and gut microbiota was evaluated in European seabass juveniles. Four diets, a control diet (CTR) and three diets containing 7.5% C. tomentosum, either untreated (COD) or pre-treated for 30 min (COD30) or 60 min (COD60), were formulated and fed for 11 weeks. Fish fed the COD30 diet showed increased intestinal lipid peroxidation, higher plasma lysozyme activity, and reduced total glutathione, compared with CTR and COD. In parallel, distal intestine inflammatory (TNF-α, IL-10, IL-1β) and apoptotic (CASP3, CASP9) gene expression was downregulated relative to COD diet, suggesting a dissociation between oxidative damage and inflammatory activation. In fish fed COD60, intestinal lipid peroxidation plasma lysozyme activity were reduced and distal intestine inflammatory and apoptotic gene expression was lower than in COD diet. Hepatic oxidative stress markers were not affected by dietary treatment. DGGE analysis revealed no significant changes in microbial richness or diversity, although COD30 increased digesta community similarity. Overall, high-solid-loading alkaline pre-treatment of C. tomentosum for 60 min mitigated the oxidative and inflammatory/apoptotic impacts associated with dietary inclusion of the untreated macroalga, supporting ingredient processing as a strategy to improve the functional value of macroalgal aquafeeds.