Vacuum steam-deodorized fish oils oxidized under flourescent light (950 lux) at 21°C initially developed green flavors which were caused principally by t,c-2,6-non-adienal, but some green-type flavor notes were contributed byt-2-hexenal and 1,c-5-octadien-3-one. Diminishment of green flavor notes resulted from the depletion of 2,6-nonadienal and the formation ofc-4-heptenal (>1 ppm) which contributed oxidized, burnt flavor notes. Concomitant formation oft,c,c-andt,t,c-2,4,7-decatrienal (>1 ppm) yielded characterizing burnt/fishy or cod liver oil-like flavors in fish oils. Two unidentified compounds exhibiting minnow-bait-bucket and trout-like odor qualities, respectively, were encountered in oxidizing fish oils. Hexanal, 2,4-heptadienals and 2,4-decadienals contributed general oxidized, painty flavors to fish oils