Effect of temperature and dissolved oxygen on swimming performance in crucian carp

Changing environmental conditions may affect the swimming performance of fish by affecting energy sources through changes in temperature and concentration of dissolved oxygen (DO). It has become increasingly important to investigate the effect of temperature and DO on the swimming performance of fish species as hypoxia in aquatic environments worldwide is increasing due to the effects of anthropogenic global warming. To test how different swimming modes respond to thermal and DO changes, 3 measures of swimming performance were tested: critical swimming speed (U-crit), constant acceleration speed (U-cat), and maximum speed during a fast-start (U-fast). The changes in these 3 aspects of swimming performance in juvenile crucian carp Carassius carassius were quantified at 2 different temperatures (10 and 20 degrees C) and 3 different DO concentrations (2.5, 5, and 9 mg l(-1)). U-cat was ca. 110 to 156% of U-crit, whereas U-fast was ca. 394 to 472% of U-crit, depending on the experimental conditions. Temperature had a significant effect on all 3 measures of swimming performance, whereas DO had significant effects only on Ucat and Ucrit (U-crit but not U-cat decreased in the 2.5 mg l(-1) DO group). The active metabolic rate (MO2active) under the different experimental conditions suggested that the decrease in Ucrit at a lower temperature and DO level could be partially explained by a decrease in oxygen uptake capacity. These results indicate that all 3 swimming measurements should be used when addressing how temperature affects swimming performance.