| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2006: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2005: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2004: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
Some indicators of environmental stressors were examined in the development of healthy fish seedling production. In addition, ontogenic changes in the stress response to environmental stressors were studied in some kinds of fish in their lifespan from larvae through the juvenile stage. At first, Pagrus major juveniles were subjected to low oxygen, high and low temperatures, hypo-and hyper-salinity. The specific activities of heat shock factor (HSF), glucocorticoid receptor (GR) and cortisol level as stress indicators in the fish were compared. The cortisol concentration was increased just after stress exposure, but the specific activities of HSF and GR gradually tended to become elevate. Fish showing both high and low tolerance to stress exposure were also selected and determined to be stress indicators. HSF and GR activities in high tolerance fish tended to be higher than those in the low tolerance fish. The HSF, GR and cortisol level were suggested to be good indicators to check in fish. Next, the ontogeny of hypoxia tolerance and stress response were studied in Pagrus major, Paralichthys olivaceus, Takifugu rubripes and Thunnus orientalis larvae and juveniles. The results indicated that around the stages of flexion and post-flexion larvae in fish, metabolic rates and/or energy metabolism were the highest, and consequently hypoxia tolerance was the lowest. Finally, ontogenic changes in some stress tolerances and the response to this were examined in larvae and juveniles. It was found that at the early juvenile stage all of the tolerances and the cortisol level were increased. The effects of cortisol immersion on various stress tolerances in larvae were also tested. The response of the survival rate, cortisol concentration and GR activity to stressors showed a tendency to increase as a result of cortisol immersion. It was therefore suggested that cortisol has an important role in adaptation to environmental stressors.
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