This study aimed to evaluate the efficacy of green and red macroalgae extracts and β-glucans on the disease resistance and growth performance of Nile tilapia (Oreochromis niloticus) in long-term dietary use. An algae-based marine sulphated polysaccharides (MSP) extracts, from Ulva sp. and Solieria chordalis, and 60% purified yeast-based β-glucans available in the market were used in the feeding trial. Fish weighting ~4 g were reared at 26-28 °C, and average dissolved oxygen 6 mg/L. Fish were assigned to 4 different dietary treatments and 6 replicates (tanks of 60 L): Control; Algae MSP 0.3%; β-Glucan A 0.1% and β-Glucan B 0.1%. Fish were stocked at a density of 15 fish/tank (90 fish/treatment) and fed twice a day for 110 days. At the end of the feeding period, all fish were weighed to assess growth, and 8 fish per treatment were sampled for innate immune response analysis. Another 6 fish per treatment were exposed via immersion to a bacterial solution containing Aeromonas hydrophila and Streptococcus agalactiae. Following 24 hours, gill samples were collected for histopathological evaluation using a diagnostic scoring system performed by a specialized laboratory. Additionally, a third group of 12 fish per treatment was intraperitoneally challenged with the same bacterial solution, and survival was monitored for 7 days. Data were analyzed using one-way ANOVA with means compared by Duncan’s test (p<0.10) or Kaplan-Meier for survival data (SigmaPlot, Systat Software, San Jose, CA, USA). Tilapia fed Algae MSP showed the most consistent results overall: final weight gain was 3.4% higher than the control (p = 0.071); lysozyme activity was 109% higher (p<0.001); and superoxide anion production (NBT assay) was significantly higher in all supplemented groups compared to the control (p<0.001). Myeloperoxidase activity was highest in the β-Glucan B group, while hemolytic complement activity was greatest in the β-Glucan A group. Algae MSP was the only treatment that showed significantly higher survival after bacterial challenge (50% vs. 16.7%) compared to control. Although survival was numerically higher in fish fed β-Glucan A (33.3%) and B (25%), differences were not statistically significant. Gill histopathological scores were 1.15 (Control), 0.17 (Algae MSP), 0.42 (β-Glucan A), and 0.30 (β-Glucan B), representing a 85% reduction in tissue damage compared to the challenged control. In conclusion, Algae MSP demonstrated the most consistent overall performance, excelling in growth, innate immunity, gills protection, and survival meanwhile β-Glucans showed intermediate effects across evaluated parameters. The results highlighed the algae-based solution as a tool for strengthening natural defenses in aquaculture due to its broader benefits in long-term use.
Keywords: Health, Survival, Marine sulfated polysaccharides.