1Erimo Research Branch, Hokkaido Fish Hatchery, Erimo, Hokkaido 058-0202, 2Hokkaido Fish Hatchery, Eniwa, Hokkaido 061-1433, 3Mashike Research Branch, Hokkaido Fish Hatchery, Mashike, Hokkaido 077-0216, 4Makkari Research Branch, Hokkaido Fish Hatchery, Makkari, Hokkaido 048-1602, Japan
We evaluated whether triglyceride and glycogen levels in the liver of masu salmon Oncorhynchus masou fry were suitable indices of starvation. Triglyceride levels gradually declined during the spring for each of four groups in a hatchery (wild-origin fed fry, wild-origin unfed, hatchery-origin fed, and hatchery-origin unfed), as well as for hatchery-origin fry from a river, while glycogen levels did not. Triglyceride levels also declined gradually during winter for wild-origin fish brought back to the hatchery, regardless of whether they were fed. Glycogen levels declined rapidly for those fish that were not fed. Regardless of the season, unfed fish began to die when triglyceride levels reached a level significantly lower than that found among fed fry or fry caught in the river. We conclude that triglyceride content is a useful index of hard starvation for underyearling masu salmon. In contrast, seasonal patterns must be considered before glycogen levels can be used as an index of starvation.