A 70-day feeding trial was conducted to investigate the effects of replacement of fish oil by vegetable oil on hepatic and intestinal histology of rainbow trout,Japanese seabass and yellow croaker,with initial weight (11.24±0.07),(18.60±0.36) and (8.93±0.21) g,respectively.Three isonitrogenous (crude protein 41%) and isolipidic (crude lipid 12%) practical diets were formulated to contain graded levels of vegetable oil blend (0%,50% and 100% dry weight) by supplementation of soybean oil and inseed oil (1:1).0% vegetable oil blend group was treated as the control group.The three artificial diets were named FO,FV and VO,respectively.The feeding trials were conducted in indoor freshwater system (rainbow trout) or sea floating cages (Japanese seabass and yellow croaker).Results showed that increased lipid vacuoles in hepatocytes cytoplasm and serious intestinal inflammation was induced by increasing level of fish oil replacement in all three fish species.Among the three fishes,liver and intestinal structure of yellow croaker was affected the most seriously by the vegetable oil.