Scientific observations on fishes incidentally caught during commercial krill fisheries by F/V Niitaka Maru (5306t) were made from August 6 to September 9, 2004 to the north of South Georgia Island. Among 100 net hauls quantitatively examined, a total of 12 species belonging to 6 families of by-catch fishes were occurred in 76 trawl catches. The family Myctophidae, the most abundant taxa during the present survey, were found in 61% of hauls examined. Although only one species, Lepidonotothen larseni, was captured as by-catch of the Nototheniidae, the Nototheniidae were the next in abundance and found in 25% of hauls. Length frequency distribution of by-catch of L. larseni shows this species is composed of at least 3 different year classes. Similar pattern is also found in Gymnoscopelus nicholsi of the Myctophidae. At least in the net hauls of high krill CPUE (>20t?krill/h), few or no by-catch fish was occurred. The hauls of lower krill CPUE (<5 t?krill/h), however, did not always contain a large amount of incidental catch of fish. The negative correlation between abundance of by-catch fish and krill CPUE is not clear.