Eggs of the Japanese eel, Anguilla japonica, were obtained by hormonally induced maturation and ovulation, and then categorized as buoyant and non-buoyant types in seawater after insemination. The water content of the buoyant eggs, 93.1%, was significantly higher than that of the non-buoyant eggs, 87.5%. Furthermore, the buoyant eggs had 1.5 times more free amino acids (FAA), 573.5 mumol/g dry weight (DW), than the non-buoyant eggs, 385.8 mumol/g DW, while no significant difference in egg lipid content or protein content was found. Compared to other pelagic eggs reported in the literature, the FAA content of the buoyant eggs was relatively low, although the water content was similar. These results suggest that there is a close relation between the quality of Japanese eel eggs obtained by typical hormonal inducement and the FAA content of the eggs, but the roles of FAA in the acquisition of egg buoyancy and fulfilling the early nutritional requirements are comparatively minor. (C) 2003 Elsevier Science B.V. All rights reserved.