The search for natural immunotherapeutic agents has become increasingly important for fish disease treatment and prophylaxis. The present research explored the effects of macro- and microalgal extracts on zebrafish juvenile growth and immune status. A plant-based diet was used as a control (diet C), and seven other diets were prepared similar to diet C, supplemented with 10 g Kg−1 of each algal extract (Fucus vesiculosus, F; Nannochloropsis gaditana, N; and Ulva rigida, U), or a combination of extracts (diets FN, FU, NU and FNU). A fishmeal-based diet was included as a positive control (diet C+). Diet C+ outperformed the remaining dietary treatments, growth-wise. None of the extracts improved diet C negative effects. However, the inclusion of U. rigida and N. gaditana extracts promoted an immunomodulatory action after 1 week of trial, by upregulating cytokine expression. This effect subsided after 30 days, suggesting tolerance may be developed over time. In contrast, effects on growth-related genes were still observed after 5 weeks of feeding F, N, U and FN diets. Algal extract dietary inclusion did not compromise intestinal integrity. These findings support the potential of algal extracts as functional feed additives during short periods (<30 days) to enhance immunomodulation.

Fincanced by the Foundation for Science and Technology (grants number: SFRH/BD/114995/2016,EBRALGRE_ BM_2019-003 UID/Multi/04423/2019 POCI-01-0145-FEDER-007621 PTDC/CVT-WEL/5207/2014).

14 Pág. Centro de Investigación en Sanidad Animal (CISA)

Peer reviewed