Oxygen Consumption of Ayu Larvae in Fasting Condition

孵化直後から孵化後55日までのアユ仔魚を絶食させ、その代謝の状態を調べた。50%の仔魚が生残する日数は3日から6日間であった。絶食中のアユ仔魚の酸素消費量は減少する場合よりも、増加する場合の方が多く、アユ仔魚の場合は絶食耐性はごく限られた発達のステージのみに現れ、むしろ異常な代謝の亢進を示す場合の方が多いことが明かになった。C/N比は絶食期間の最後まで活力を維持して生き残った個体と摂餌をしている個体との間で有意な差を示さなかった。瀕死の状態にある個体ではC/N比は摂餌個体とは有意に異なり、その変化はエネルギー源としての炭水化物の涸渇と筋肉タンパクをエネルギー源に変えている代謝の状態を反映していた。組織学的検査においても肝臓中のグリコーゲンの消失、筋肉組織や膵組織の壊死が絶食が続くと観察された。

The oxygen consumption and nutritional condition of ayu (Plecoglossus altivelis) larvae under a fasting condition were investigated by the use of the larvae from immediately after hatching (Day 0) until 62 days after hatching (Day 62). In the fasting condition, 50% or more of the larvae at each growth stage survived for 3 to 6 days. During the fasting period, the fasted larvae often showed significantly higher oxygen consumption rates per dry body weight (OCR) for one or two days (the larvae groups fasted from Day 0, 5, 10, 15, 20, 25, and Day 45) and 7 days (Day 55 group) than those before fasting, while the fasted larvae in the Day 5, 40, and Day 50 groups exhibited significantly lower OCRs for one to three days than those before fasting. There were no significant differences in the carbon to nitrogen ratio (C/N ratio) between the larvae before fasting and the live larvae on the last fasting day in any group except the Day 55 group. The moribund larvae exhibited significantly lower (Day 10 and 15 groups) and higher (Day 50 group) C/N ratios than the larvae before fasting. Decrease in glycogen in the liver, atrophy of liver cells, and marked necrosis of the pancreas and the skeletal muscle were observed in the fasted larvae.