Colaconema daviesii attenuates acute and diet-induced intestinal inflammation and reduces intestinal permeability in vivo in zebrafish.

Marine macroalgae are increasingly explored as functional feed ingredients in aquaculture because they contain bioactive compounds with immunomodulatory and antioxidant properties that may contribute to fish health. However, the biological activities of many red macroalgae remain poorly characterized. Colaconema daviesii is a cultivable filamentous red macroalga whose effects on inflammatory responses in fish have not been investigated. Here, we characterized cultured C. daviesii biomass and evaluated its anti-inflammatory activity in vivo in zebrafish. Biochemical analyses identified phycobiliproteins, including phycoerythrin, phycocyanin, and allophycocyanin, together with chlorophyll, carotenoids, and fatty acids. The functional in vivo assay determined that C. daviesii did not alter peripheral neutrophil abundance under basal conditions, indicating no immunostimulant effect. In contrast, treatment significantly reduced neutrophil recruitment following caudal fin injury and decreased intestinal neutrophil accumulation during sustained exposure to an inflammatory diet. In the intestinal inflammation model, C. daviesii also reduced the increase in intestinal permeability, measured by extraintestinal passage of 3-kDa dextran, to levels comparable to those of control-diet larvae. These results demonstrate in vivo anti-inflammatory activity of C. daviesii across acute tissue injury and sustained diet-induced intestinal inflammation and show that this response is accompanied by reduced intestinal permeability. The capacity of C. daviesii for controlled cultivation, together with its effects under inflammatory conditions, supports further evaluation of its biomass as a functional ingredient for intestinal health in aquaculture.