Gonad Maturation and Dynamics of Crude Lipid Content in the Body of Yellowtail During the Spawning Season

Abstract

Gonad maturation and changes in lipid content in the liver, viscera, lateral muscle and gonad of 3 year old yellowtail were investigated by 38 specimens taken from March 17 to May 25. The body length of the specimens ranged from 62.5cm to 76.5cm in the wild fish, and from 68.1cm to 84.0cm in the cultured fish. The gonad of the wild or cultured fish was complete by matrue from the middle of April to early in May, and evidently degenerated after the last third of May. The mature gonad was found to be relatively smaller in the cultured fish than in the wild fish migrating for spawning along the coast of Tosa Bay.
Total lipid in the lateral muscle, liver, viscera and gonad was remarkably greater in the cultured fish than in the wild fish. It was about 145g per kg of body weight in the former and about 45g in the latter when gonad matruation was complete. After the gonad began to degenerate, it showed a distinct decrease, about 40g compared with the mature stage. The bulk of crud lipid in the body of yellowtail was located in the trunk muscle.