Supplementing the diet of Nile tilapia (Oreochromis niloticus) with microalgae Nannochloropsis oculata and Phaeodactylum tricornutum enhanced immune function, lipid profile, and resistance to Edwardsiella tarda infection.

UNLABELLED: The aim of the present study was to evaluate the effects of dietary supplementation with the microalgae Nannochloropsis oculata and Phaeodactylum tricornutum, either separately or in combination, on growth performance, lipid profile, haematoimmunological parameters, and resistance to Edwardsiella tarda infection in Nile tilapia (Oreochromis niloticus). A total of 960 juvenile Nile tilapia (2.87 ± 0.68 g and 5.65 ± 0.16 cm) were allocated to 24 experimental units (n = 40) and fed six experimental diets for 60 days: DC0% (no microalgae inclusion), DN0.5% (0.5% N. oculata), DN1% (1% N. oculata), DP0.5% (0.5% P. tricornutum), DP1% (1% P. tricornutum), and DPN1% (0.5% N. oculata + 0.5% P. tricornutum). After the feeding period, fish were challenged with E. tarda (2 × 10⁸ CFU mL⁻¹). Microalgal inclusion increased significantly (p < 0.05) dietary contents of phenolic compounds, flavonoids, tannins, and antioxidant potential of diets without affecting fish growth. The DP1% and DPN1% diets increased significantly (p < 0.05) eicosapentaenoic and docosahexaenoic acid levels and reduced monounsaturated fatty acids and ∑saturated fatty acids in muscle, thereby improving the lipid profile and flesh quality. Following infection, reductions in erythrocytic parameters were observed, along with increases in lymphocyte, monocyte, basophil, neutrophil, and thrombocyte counts, as well as higher (p < 0.05) agglutination and antimicrobial titres, total plasma protein, and immunoglobulin levels in the DP1% and DPN1% groups. Survival was higher in the microalgae-supplemented groups, particularly in DPN1% (91.67 ± 1.8%) compared with the control (65.0 ± 2.0%). Supplementation with DP1% and DPN1% improved haematoimmunological responses, lipid composition, and resistance to E. tarda in Nile tilapia.

SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11259-026-11218-z.