Atlantic Salmon (Salmo salar) CCL4 (C-C motif chemokine ligand 4, also referred to as an MIP-1–like chemokine in teleost fish) is a pro-inflammatory chemokine involved in recruitment and activation of immune cells during innate immune responses. Similar to mammalian CCL4, salmon CCL4-like chemokines function to attract macrophages, neutrophils, and lymphocyte-like cells to sites of infection, tissue injury, or inflammatory stimulation through chemokine receptor pathways related to CCR5-like receptors in fish. In Atlantic salmon, CCL4 expression is induced in immune tissues such as the spleen, head kidney, gills, and mucosal surfaces including skin and intestine following pathogen exposure or inflammatory signaling. This chemokine plays an important role in defense against bacterial pathogens such as Aeromonas salmonicida and Vibrio species, as well as viral diseases including infectious salmon anemia virus (ISAV) and salmonid alphavirus, where recruitment of immune cells to infected tissues contributes to pathogen clearance and immune activation. Proper regulation of CCL4-mediated leukocyte trafficking supports effective inflammatory responses and tissue defense, while excessive expression may contribute to inflammatory pathology. Characterization of Atlantic salmon CCL4 supports research into teleost immune signaling, host–pathogen interactions, and development of disease resistance strategies in aquaculture, providing insight into conserved chemokine-mediated immune mechanisms across vertebrate species.