Tumor necrosis factors (TNFs) are a group of cytokines that play critical roles in regulating a diverse range of physiological processes in vertebrates.TNFs function by activating a large number of structurally related receptors,leading to TNF mediated biological processes which are evolutionarily conserved.Fish have a much diversified TNF family,partly due to the whole genome duplication events which have occurred in this lineage,providing an excellent model to investigate the neo-and subfunctionalised properties of TNF superfamily.Fish possess most of the TNFs and receptors found in mammals and also some homoiogues exclusively present in fish.It seems that TNFSF4 (OX40),TNFSF7 (CD27) and TNFSF8 (CD30) and their cognate receptors are absent in teleosts.It has been shown that fish viruses are able to produce TNFR homologues to establish infection by manipulating the host immune system.Understanding the roles of TNFSFs in fish immune defence and the pathogenesis of fish diseases will provide insights into the functions of TNFSFs from an evolutionary perspective and better strategies for improving fish health and welfare in aquaculture.This review summarises recent advances in the study offish TNF biology and focuses on the molecular properties and immunological functions of the TNF and TNFR superfamily.