动物必须从外界环境摄入能量以维持正常的生长和繁殖。当动物摄取不到维持其基本生命活动所必需的食物时，其存活、生长、发育都会受到影响。在饥饿胁迫下，动物必须降低自身能量消耗，同时调动抗氧化防御系统以应对饥饿可能导致的氧化压力。恢复喂食后，动物快速摄入能量，但也可能面临快速生长带来的过氧化风险。龟鳖类动物具有出色的耐饥饿能力，其有氧代谢水平较低，但抗氧化能力却接近甚至高于部分哺乳动物。有关长期饥饿和恢复饱食过程中龟鳖类动物的呼吸代谢和抗氧化防御水平如何变化，尚不太清楚。据此，本论文拟研究以下科学问题：1、不同龟鳖的体重、呼吸代谢和抗氧化防御系统如何响应长期食物剥夺与恢复喂食？2、长期食物剥夺和恢复喂食作为能量获得完全不同的两个时期，机体在生长速度、呼吸代谢、抗氧化防御上于两个阶段的差异，以及三项生理指标之间是否存在内在联系？ 为研究上述问题，我们以中华草龟（Chinemys Reevesii）、拟鳄龟（Chelydra serpentina）和中华鳖（Pelodiscus sinensis）作为实验对象，从养殖场购入三种淡水龟鳖的2龄幼体各40只（n=40），在27±1℃下于实验室内驯化4周。饥饿组S为完全禁食4周，恢复组RS为完全禁食4周后恢复喂食2周；基底对照组B、饥饿对照组SC、恢复对照组RC不禁食，其余条件和实验组保持一致，每个处理组8个样本（n=8）。处理前后测定动物体重，每个处理结束后观测静止代谢率，然后取脑、肝、肾，测定三种龟鳖体内呼吸代谢相关酶（SDH、COX）活力，测定脂质氧化损伤程度（MDA）及其总抗氧化力（TAOC）、抗氧化酶（SOD、CAT、GPx）活力，比较三种龟鳖在长期食物剥夺和恢复喂食过程中体重、呼吸代谢和抗氧化防御系统的变化。 主要结果和结论如下： 1、中华草龟、拟鳄龟和中华鳖体重和SGR呈现相同的变化趋势，即在食物剥夺期间出现显著下降，恢复喂食后大幅上升，并且拟鳄龟体重增长和SGR略高于其他两种龟鳖。 2、三种龟鳖呼吸代谢对长期食物剥夺作出响应：RMR在长期食物剥夺过程中均出现下降，以适应无法摄入能量的不良环境，恢复喂食后三种龟鳖RMR均维持在较低水平。中华草龟SDH酶活在两个时期显著下降，其他两种龟鳖无显著变化。三种龟鳖COX酶活力无显著变化。 3、三种龟鳖各组织中MDA含量均无显著变化，即未受到氧化损伤。中华草龟和中华鳖肝脏中TAOC在恢复喂食时期显著升高，拟鳄龟肝脏中未出现显著变化，推测拟鳄龟对饥饿的适应能力更强。 4、在长期食物剥夺时期，中华草龟和中华鳖抗氧化酶活力做出积极响应：中华草龟各组织SOD、脑组织CAT、肾脏中GPx，以及中华鳖肾脏、脑组织SOD、脑组织GPx酶活力显著上调。拟鳄龟各组织抗氧化酶活均未出现显著上升。 5、恢复喂食后，中华草龟和中华鳖大多数抗氧化酶酶活力恢复至对照水平，仅中华草龟肝脏SOD、肾脏GPx，中华鳖脑组织中SOD酶活显著高于对照；而拟鳄龟多数抗氧化酶：各组织SOD、脑组织中CAT均显著高于对照。结合SGR结果，原因可能是拟鳄龟快速生长造成ROS过量积累。

Animals must absorb energy to maintain normal growth and reproduction. When animals can’t gain sufficient food to support their basic life activities, their survival, growth and development will be affected. Under the stress of starvation, animals must reduce their energy consumption and mobilize the antioxidant defense system to cope with the oxidative stress caused by starvation. When food is sufficient again, animals tend to absorb energy quickly, but they may face the risk of peroxidation of rapid growth. As the typical species of resistant to stress, turtles have low level of aerobic metabolism but their antioxidant capacity is close to or even higher than some mammals. While how the respiration metabolism and antioxidant defense system of turtles respond during long-term starvation and refeeding is less clear Based on the above background, the following scientific questions are raised in this essay: 1. How do body mass, respiratory metabolism and antioxidant defense system of turtles respond to long-term food deprivation and refeeding? 2. Is there any relationship between growth rate, respiratory metabolism, and antioxidant defense system? To answer the questions above, we chose these freshwater turtle species, the Chinese three-keeled pond turtle Chinemys Reevesii, the Common snapping turtle Chelydra serpentina and the Chinese soft-shelled turtle Pelodiscus sinensis as experimental animals. We arranged 40 animals (age 2) of three species of turtles. All animals were acclimated in the laboratory with the temperature of 27±1 ℃ for 4 weeks. The experimental group S was completely fasted for 4 weeks, RS was completely fasted for 4 weeks and refeed for 2 weeks. The control group B, SC and RC did not fast, and the remaining conditions were same as the experimental group. Each group has 8 samples(n=8). All animals were weighed every treatment. RMR mere measured and tissues (liver, kidney and brain) were token after every treatment. Body mass, SGR, MDA, TAOC, activities of respiratory metabolism-related enzymes (SDH, COX) and antioxidant enzymes (SOD, CAT, GPx) were measured. All statistics were to compare the metabolic adaptation and antioxidant defense responses of three turtle species to long-term food deprivation and refeeding. The main results and conclusions were summarized as below: 1.Changes of the body mass and SGR of C.reeverii, C.serpentina and P.sinensis showed a similar pattern, that is, the body mass decreased significantly in the food deprivation period, and increased largely after refeeding. The weight gain and SGR of C.serpentina were slightly higher than the other two species. 2. The RMRs of three turtle species decreased in the period of long-term food deprivation to adapt to the adverse environment in which animals can’t get food. After refeeding, RMRs of the turtles remained at a low level. In C.reeverii, SDH activity decreased significantly in the two periods, but there was no significant changes in the two other turtle species. There were no significant changes in COX activity. 3. MDA concentration showed no significant change, which means, none of them suffered from oxidation damages in tissues. Additionally, TAOC level in the liver of C.reeverii and P.sinensis increased significantly during the refeeding period, while there were no significant changes in the liver of C.serpentina. 4. In the long-term food deprivation, the activities of most antioxidant enzymes of C.reeverii and P.sinensis activated. However, there was no significant increase in activity of antioxidant enzyme in all tissues of C.serpentina. 5. In the refeeding period, acitivities of most antioxidant enzymes of C.reeverii and P.sinensis recovered to the control level. In C.serpentina, SOD activity in all tissues and CAT activity in brain were significantly increased. It may suggest that the rapid growth of C.serpentina may cause excessive accumulation of ROS.