Affect of chronic and acute stress on growth and survival of hatchery-reared Japanese flounder juveniles

1. 在3种不同的饲养密度下，对定居后的幼鱼进行3个月的饲养。试验结束时，三种处理间幼鱼血浆皮质醇水平无显著差异，但过度拥挤条件下饲养的幼鱼肾间细胞核面积显著增大。这表明慢性压力促进了皮质醇的代谢。为了研究慢性应激下ACTH分泌能力的变化，在底部没有沙子的过度拥挤条件下饲养幼鱼12周。在本实验中，ACTH分泌细胞的核面积明显增大。因此，在细胞水平上，幼鱼的形态变化被认为是慢性应激的原因。为了确定对急性应激的耐受性，将比目鱼幼鱼暴露在空气中。暴露于空气15分钟和20分钟的幼虫死亡率分别约为65%和30%。所有人暴露在空气中30分钟后全部死亡。每天暴露在空气中10分钟，连续5天，再暴露15分钟，所有幼鱼都存活了下来。然而，在暴露之前没有受到压力的鱼的存活率只有13%。3%。由于在存活的幼鱼中没有观察到暴露后的皮质醇升高，因此表明对急性应激的耐受性与皮质醇反应有关。运输搬运对幼鱼死亡率的影响小体幼鱼（35 mm TL）在从生长场搬运到放养区搬运过程中表现出明显的应激反应（皮质醇升高），死亡率高。认为运输是造成小鱼放生后死亡的因素之一。

1. Physiological and morphological response for chronic stressPost-settlement juveniles were reared for 3 months at three different rearing density. Plasma cortisol level of young fish was not different at the end of the experiment among three treatments but the nuclear area of interrenal cell of fish reared under overcrowded conditions became significantly larger. It suggested that chronic stress promoted metabolism of cortisol. To examine a change in capability of ACTH secretion for chronic stress, juveniles were reared for 12 weeks under overcrowded conditions without sand on the bottom. In this experiment, the nuclear area of ACTH secretion cell significantly increased in size. Thus, morphological change of juveniles was recognized for chronic stress at cell level.2. Response of juveniles for lethal acute-stressorsTo determine a tolerance to acute stress, flounder juveniles were exposed to the air. A mortality of juveniles which were exposed to the air for 15 and 20 minutes was about 65 % and 30 %, respectively. All individuals were dead by 30 minutes exposure to the air. All juveniles which were exposed to the air for 10 minutes once a day for five days before 15 minutes exposure were survived. However, a survival rate of fish which were not stressed before exposure was only 13. 3 %. As a cortisol elevation after exposure was not observed in survival juveniles, it was suggested that tolerance to acute stress was related to the cortisol response.3. Effect of handling at transportation on mortalitySmall size juveniles (35 mm TL) showed clear stress response (cortisol elevation ) for handling at transportation from grow-out facility to release area and mortality rate was high. It was suggested that transportation is one factor of mortality after release for small size fish.