Species composition and abundance of by-catch fish were analyzed using the fish by-catch samples collected by scientific observers onboard Japanese commercial krill fishing vessels in the north of South Georgia during the austral winter from 2002 to 2008. A total of 19 species belonging to 8 families were identified in the by-catch samples, among which the 3 species, Krefftichthys anderssoni, Lepidonotothen larseni and Champsocephalus gunnari, were recorded in every year from 2002 to 2008, and also the most abundant. Different life stages of K. anderssoni, Gymnoscopelus nicholsi, C. gunnari and L. larseni from larvae to adults were found, suggesting that these species may have their nursery ground around South Georgia. The length frequency distribution of C. gunnari varied with years and may indicate the increase in size in recent years. Electrona antarctica was not a major component of the recent mesopelagic ichthyofauna. In contrast, P. choriodon, which is known as a South temperate species, became to dominate the recent samples. Additionally, the size distribution of P. choriodon was unimodal, indicating that the individuals probably migrated from the population in northern warmer areas. Since the distribution patterns and biological peculiarity of fish are related to oceanographic conditions, the shifts in species and size composition may demonstrate oceanographic and climatic changes in the Antarctic Ocean. Long-term monitoring of ichthyofauna through the scientific observer program and close examination of the biological samples would provide important information on environmental fluctuations in the Antarctic Ocean.