Subsequent Changes in the Thymus of Ayu Plecoglossus altivelis Reared from Juveniles with Temperature-induced Differential Thymus Growth

抄録

The temperature of water used to rear juvenile stages of ayu affects the development of the thymus. ​However, subsequent differences in the thymus in adults after rearing juveniles at different temperatures are unclear. ​We analyzed thymus development of ayu grown at a constant water temperature of 15°C from juveniles reared at different water temperatures. ​Juvenile ayu weighed at 0.6 g and 1.4 g were reared at different temperatures (10°C, 12°C, 15°C, 18°C and 22°C) for 64 days and 54 days, respectively, and then held at 15°C for analysis of the thymus development. ​Thymus volume was measured by computed tomography and thymus development of experimental fish was evaluated as the ratio of thymus volume to body length. ​The thymus volume ratios of juveniles immediately after rearing at lower water temperatures (10°C, 12°C) were higher than in those reared at the higher temperatures (18°C, 22°C). ​These levels of thymus volume ratio were preserved in grown ayu continuously reared at 15°C. ​After the summer solstice, the thymus began to atrophy and no longer exhibited differences among the experimental groups. ​Thus the thymus formed at the juvenile stage retains its morphological properties until the summer solstice.