Zebrafish (Danio rerio) Interleukin-13 (IL-13) is a type 2–associated cytokine identified in teleost fish that shares functional similarities with mammalian IL-13 and contributes to regulation of mucosal immunity, alternative macrophage activation, and tissue repair. Zebrafish possess IL-4/13–like cytokines (commonly termed IL-4/13A and IL-4/13B) that are considered evolutionary homologs of mammalian IL-4 and IL-13, reflecting the divergence of these cytokines following genome duplication events in teleosts. These cytokines signal through receptor complexes homologous to IL-4Rα/IL-13R–type chains and activate STAT6-dependent pathways, promoting anti-inflammatory macrophage polarization, modulation of pro-inflammatory cytokine production, and support of epithelial barrier function. In zebrafish, IL-4/13–like cytokines are induced during helminth and bacterial infections, tissue injury, and models of intestinal inflammation, where they contribute to resolution of inflammation and tissue remodeling. Because zebrafish are widely used for live imaging of immune cell dynamics, genetic manipulation, and high-throughput drug screening, characterization of IL-13–like signaling supports studies of Th2-like immune polarization, macrophage plasticity, fibrosis, and cytokine network evolution. As a conserved regulator of type 2–associated immune responses, zebrafish IL-4/13–like cytokines provide valuable comparative insight into the evolutionary origins and functions of IL-13–mediated immunity relevant to human allergic and fibrotic diseases.