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Crucian (Carassius auratus auratus) damage caused by pressure changes under subatmospheric conditions*

LI Hai-Feng① SHAO Qi① WU Yu-Lin ①** CHENG Hong② CHEN Mao-Sheng② GUO Mei-Zhu① (① Department of Thermal Engineering, Tsinghua University, Beijing 100084, China) (② School of Life Science, Peking University, Beijing 100871, China)  
With increasing awareness of environment protection, the damage to fish caused by hydraulic machinery is attracting more and more scientific interest. We conducted experiments to study damage to the crucian (Carassius auratus auratus) caused by pressure changes under subatmospheric conditions. In the experiments, we used a gas access system composed of a pressure vessel, a vacuum pump and an air compressor to simulate the pressure changes in hydraulic structures, and a digital signal system composed of a pressure sensor, amplifier, A/D card and a computer to obtain pressure-time data. Crucians grouped according to body length were placed under these various conditions. After the exposure of each group to different pressure conditions, damage to fish and the corresponding pressure changes were recorded. Some injured fish were anatomized and histological observation was also conducted to determine the main damage. The results demonstrate that crucians can be seriously injured or even killed by pressure changes with high pressure derivative relative to time, resulting in partial or completely injured swim bladders and obvious bleeding under the kidney capsule and liver-pancreas, especially in the marginal region. We conclude that controlling the pressure derivative with respect to time in hydraulic passages can effectively prevent such injuries. An estimate of the maximum derivative of pressure with respect to time that allows crucians to pass through hydraulic passages safely is provided, this could be a criterion for the design of new environmental-friendly hydraulic structures protecting fish culture operations. The mechanism whereby fish are damaged by pressure changes is also discussed [Acta Zoologica Sinica 49(1):67-72, 2003].
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