Seasonal variation of phosphatidylcholine hydroperoxides in blood of sweet smelt Plecoglossus altivelis.

Sweet smelt was reared at two fishery experimental stations for 5 months from June to October. Every 2 weeks blood was collected from the caudal vessels and, subsequently, the phosphatidylcholine hydroperoxide contents and the fatty acid compositions in the blood were determined by high-performance liquid chromatography and gas chromatography, respectively. The seasonal variation of the contents of accumulated hydroperoxides and fatty acids in the sweet smelt blood were observed in both experimental stations. Sweet smelt started performance of cucumber-like or watermelon-like aroma in the middle of July and the aroma was enhanced in August. The content of phosphatidylcholine hydroperoxides and the amount of total fatty acid in the fish blood, in terms of possible precursors of volatile compounds, were also extremely high in the same period. According to lipid peroxidation mechanisms, the strong characteristic aroma of sweet smelt during July to August might be due to the high contents of accumulated lipid hydroperoxides and polyunsaturated fatty acids in their tissues.