Atlantic Salmon (Salmo salar) Tumor Necrosis Factor Alpha (TNF-α) is a proinflammatory cytokine that plays an important role in innate immune responses, inflammation, and host defense against pathogens in teleost fish. TNF-α belongs to the tumor necrosis factor (TNF) superfamily, which in vertebrates includes molecules such as TNF-α, TNF-β (lymphotoxin), Fas ligand (FasL), CD40 ligand (CD40L), and TRAIL, all involved in regulating immune signaling, apoptosis, and inflammatory responses. In Atlantic salmon, TNF-α is primarily produced by activated macrophages, monocytes, and other immune cells following infection, tissue injury, or exposure to pathogen-associated molecular patterns. TNF-α signals through TNF receptor homologs that activate intracellular pathways such as NF-κB and MAPK, leading to the induction of proinflammatory cytokines, antimicrobial responses, and immune cell recruitment. In salmon, TNF-α plays a critical role in defense against bacterial and viral pathogens common in aquaculture, including Aeromonas salmonicida, Vibrio species, and infectious salmon anemia virus (ISAV), by promoting inflammatory responses and activation of innate immune defenses. TNF-α is also involved in regulating immune responses in key mucosal tissues such as the gills, skin, and intestine, which serve as major pathogen entry points in aquatic environments. Because Atlantic salmon is an important aquaculture species, characterization of salmon TNF-α supports research on fish immunology, host–pathogen interactions, and disease resistance, contributing to improved understanding of immune regulation and health management in aquaculture systems.