Zebrafish IL-17A (Interleukin-17A) is a pro-inflammatory cytokine belonging to the IL-17 family that plays an important role in host defense and inflammatory responses in zebrafish (Danio rerio). Teleost fish possess IL-17A/F–like genes that share functional similarity with mammalian IL-17A and are expressed by lymphocyte-like cells and innate immune populations in response to microbial infection and immune stimulation. IL-17A in zebrafish acts on epithelial and stromal cells to induce expression of pro-inflammatory cytokines, chemokines, and antimicrobial peptides, promoting neutrophil recruitment and enhancing mucosal barrier immunity in gill, gut, and skin tissues. In healthy zebrafish, basal IL-17A expression is generally low but increases during bacterial, fungal, and parasitic infections, as well as following experimental inflammatory challenge. In developmental and immunology research, zebrafish IL-17A is widely studied in models of infection, intestinal inflammation, and innate–adaptive immune crosstalk, providing insight into the evolution of Th17-like responses and neutrophil-driven inflammation in vertebrates.