Functional Algal Feeds for Aquaculture: Micro- and Macroalgae Promote Gut Recovery in Gilthead Seabream

Gut health is essential for optimal growth, immune function, and robustness in aquaculture. This study evaluated the potential of dietary supplementation with micro- and macroalgae to promote intestinal recovery following an insult. Four experimental diets were formulated for gilthead seabream (Sparus aurata) juveniles (176 ± 0.32 g): a control commercial-like diet (CTRL), and the same diet supplemented with either microalgae (Phaeodactylum tricornutum; PHA) or macroalgae (Gracilaria gracilis; GRA) at 2.5%, or a 5% blend of both (50:50; BLEND). To induce an intestinal insult, fish from each dietary group were assisted-fed with gelatine capsules containing soy saponins (CTRL + S, PHA, GRA, BLEND), while control fish received empty capsules (CTRL). After 72 h, CTRL and CTRL + S groups were fed the control diet, while PHA, GRA, and BLEND received their respective algae-supplemented diets. After 20 days, CTRL + S fish had significantly increased mucus cell numbers and submucosal cellular infiltration compared to CTRL fish, indicating intestinal disruption. PHA diet significantly upregulated igm, il10, and gpx. Fish fed GRA displayed a significant increase in mucosal vacuolation. BLEND diet showed synergistic effects, significantly upregulating il1b and pcna and reducing ALP activity. These results highlight the potential of combining micro- and macroalgae compounds to enhance gut recovery and immune activation.