In addition to physical barriers, neutrophils are considered a part of the first line of immune defense. The mechanisms that neutrophils utilize for host defense are phagocytosis, degranulation, cytokine production, and, the most recently described, neutrophil extracellular trap (NET) production. NETs are DNA structures released due to chromatin decondensation and spreading, and they thus occupy three to five times the volume of condensed chromatin. The release of NETs is the most dramatic stage in a cell death process called NETosis. Several proteins adhere to NETs, including histones and over 30 components of primary and secondary granules, among them components with bactericidal activity such as elastase, myeloperoxidase, cathepsin G, lactoferrin, pentraxin 3, gelatinase, proteinase 3, LL37, peptidoglycan-binding proteins, and others with bactericidal activity able to destroy virulence factors. Different models of NETosis have been studied so far viz, Suicidal NETosis, In vital NETosis . NETosis has been studied intensively in mammals in recent years, but very little is known about the NETosis in fish. Insight into the early origin of ETosis in invertebrates identifies it as a very ancient process and an evolutionary conserved mechanism. NET function as double edge swords of innate immunity, serving as effective antimicrobial defences, but also a putative sources of molecules with immune effector and pro-inflammatory roles, that in susceptible individuals, may promote tissue damage and autoimmunity.