With the fast development of aqua-feed industry,fish oil has seen a great shortage,which limits the sustainable development of aquaculture industry.Alternative oils are thought to be the key to solve this problem.However,decreased immune response and disease resistance have been found as the substitution level increased.The nature of fish oil replacement is actually the fatty acid replacement.Thus,a review was made on the effects of fatty acids on immune response and mechanism involved in this process.Dietary saturated fatty acids could decrease fish immunity,while optimal inclusion of n-3 long chain polyunsaturated fatty acids(LC-PUFA)and conjugated fatty acid(CLA)or enhancing the ratio of n-3 to n-6 polyunsaturated fatty acids(PUFA)were beneficial to nonspecific immune responses of fish species.There have been a lot of studies which aimed to elucidate mechanism about how dietary fatty acid regulates fish immunity.Overall,dietary fatty acid could regulate fish immunity through several pathways such as membrane structure,signal transmission,eicosanoid,cytokine and steroid etc.These indicated that fatty acid is a critical factor to regulate fish immunity.Greater efforts should be made to study mechanism involved in this process.Future studies should be emphasized from the following perspectives:how dietary fatty acid regulate transcription factor about immunity;Relationship between fatty acid composition of intestine,bacterial community structure,and immune responses;Effects of environmental factors on fatty acid metabolism and immunity of fish species;how non-fatty acid nutrients(minerals and vitamins)regulate fatty acid metabolism and fish immunity.