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

1.慢性应激的生理和形态反应定居后幼体在三种不同饲养密度下饲养3个月。试验结束时，三种处理组幼鱼血浆皮质醇水平差异不显著，但过度拥挤条件下饲养的幼鱼肾间细胞核面积显着增大。提示慢性应激促进了皮质醇的代谢。为了检测ACTH分泌对慢性应激的能力的变化，在过度拥挤的条件下饲养了12周的幼崽，底部没有沙子。在本实验中，ACTH分泌细胞的核面积明显增大。因此，幼体的形态变化在细胞水平上被识别为慢性应激。幼体对致命性急性应激的反应为了确定对急性应激的耐受性，将比目鱼幼体暴露在空气中。暴露在空气中15分钟和20分钟的幼虫死亡率分别约为65%和30%。所有人在暴露在空气中30分钟后死亡。每天暴露在空气中10分钟，连续暴露5天，然后暴露15分钟的所有幼虫都存活了下来。然而，暴露前没有受到应激的鱼的存活率只有13.由于在存活的幼鱼中没有观察到暴露后皮质醇的升高，这表明对急性应激的耐受性与皮质醇的反应有关。搬运时搬运对死亡率的影响小型幼体(35 Mm TL)在从成长设施到放养区的搬运中表现出明显的应激反应(皮质醇升高)，死亡率高。结果表明，运输是影响小型鱼类放流后死亡的因素之一。

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.