EXHAUSTION EXERCISE STRESS ON HYPOXIA AND THERMAL TOLERANCES OF THREE CYPRINID SPECIES

The hypoxia and thermal tolerances of fish are important physiological characteristics that determine their distribution, habitat change, and adaptability to climate change. While in the nature, fish are always in the process of swimming or recovery of post-exercise, whether the hypoxia and thermal tolerances change during swimming or immediately after exhaustive recovery process is unknown for fish. Thus, to study the effects of exhaustion exercise stress on fish hypoxia and thermal tolerances, we investigated three cyprinid fish species (i.e. Carassius auratus, Spinibarbus sinensis and Cyprinus carpio) living in different habitats as study cases. Hypoxia and the thermal tolerance indicators of the three fish species were measured after exhaustion exercise, respectively, to determine whether exhaustion exercise stress would affect the stress resistance of fish. In the present study, we found that body weight only affected significantly on minimal critical temperature (CT_min), and the indicators of hypoxia and thermal tolerances were different significantly between species. Moreover, exhaustion exercise stress led to a significant increase in critical oxygen tension (P_crit) of common carp and a significant increase in critical metabolic rate (CMR) of all the three species as well, but a significant decrease in point of oxygen tension for loss of equilibrium (LOE) of qingbo. Meanwhile, it also resulted in a significant decrease in maximal critical temperature (CT_max) of goldfish and qingbo. However, there was no significant effect on the species and other related measured parameters besides the fish species and their corresponding experimental parameters mentioned above. It could be said based on the results that changes in the hypoxia and thermal tolerances of fish living in different habitats are different after exhaustion exercise stress, and that fish species vary in physiological mechanisms responding to other environmental stressors following exhaustion exercise stress, which may be related to difference in their energy metabolism patterns.