Valorization of green macroalgae Ulva lactuca as a potential dietary Ingredient for stellate sturgeon (Acipenser stellatus) and sterlet sturgeon (Acipenser ruthenus)

This study evaluated the effects of Ulva lactuca, a marine macroalgae, on growth, hematology, oxidative stress, and immune markers in two sturgeon species, Acipenser stellatus and Acipenser ruthenus, in a recirculating aquaculture system. Fish were fed either a standard diet or a 10% Ulva lactuca diet (dry weight). Results showed that Ulva lactuca inclusion reduced growth performance, with specific growth rates decreasing by 19% in A. stellatus and 41% in A. ruthenus. Haematological analyses showed no significant differences (p > 0.05) between groups, though hemoglobin levels were slightly lower in A. stellatus (5.68 g/dl in the Ulva group) compared to the control (6.44 g/dl), while A. ruthenus exhibited no change (8.02 g/dl versus 7.98 g/dl). Ulva lactuca improved oxidative stress markers, as malondialdehyde (MDA) levels significantly decreased, and total antioxidant capacity (TAC) increased in both species. Lysozyme activity remained unaffected by the diet. These findings indicate that while Ulva lactuca supplementation negatively impacted growth, it improved oxidative status without adversely affecting haematological parameters, suggesting species-specific responses and the need for further investigation.