INDIVIDUAL VARIATION AND PHENOTYPIC CORRELATIONS IN SWIMMING PERFORMANCE OF JUVENILE CRUCIAN CARP

The swimming ability is a fundamental organismal trait to influence growth, survival and even the Darwinian fitness of fish. Energy metabolism involves oxygen uptake, locomotor capacity includes aerobic swimming performance and anaerobic swimming performance, which exhibits great variations in these two physiological functional traits. Trade-off may occur when these two traits can not be optimized simultaneously since aerobic and anaerobic swimming performance pose conflicting demands on the same morphological feature of design. The present study examined the intra-individual variations and phenotypic trait correlations of swimming ability of the cyprinid fish, and investigated the effects of different acceleration speed on the constant acceleration swimming capacity in the cyprinid fish. Swimming performance of the juvenile crucian carp (Carassius auratus) including critical swimming speed (U_crit), and gait transition speed (U_gt) was performed in a U_crit test. The metabolic rates including resting metabolic rate (RMR), maximum metabolic rate (MMR), aerobic scope (AS=MMR–RMR) as well as factorial aerobic scope (FAS=MMR/RMR) were measured by both of theU_crit test and the test of excess post-exercise oxygen consumption (EPOC). A constant acceleration test (U_cat) was employed to examine the U_cat and U_gt in the juvenile crucian carp at four acceleration rates (0.083, 0.167, 0.250 and 0.333 cm/s²). Our study found that U_crit were correlated with MMR and AS with the exception of RMR while U_gt was not related to any parameters of metabolic rates (MMR, AS and RMR) in the juvenile crucian carp. There were no significant difference in parameter average of metabolic traits (MMR, AS and FAS) between two induced exercise methods, and high repeatability was detected in intra-individual level between the two methods. Distinct correlations were found among traits of metabolism. The U_crit and U_gt conducted by U_crit test were smaller than those conducted by U_cat test. The acceleration rate had a determinable influence on U_cat but not U_gt. U_gt correlated positively with either U_crit or U_cat and the constant acceleration swimming capacity had repeatability among four acceleration rates. U_cat was positively correlated to the anaerobic metabolism contribution (U_cat–U_gt) by the acceleration swimming test at three acceleration rates with the exception of 0.333 cm/s². However, the aerobic metabolic capacity (U_gt) was negatively related to the anaerobic metabolic capacity (U_cat–U_gt) in the juvenile crucian carp by the U_cat test. The study suggested that no methodological difference could be found in aerobic capacity by the test of U_crit and EPOC, and that correlation among traits of energy metabolism and constant individual difference in acceleration swimming performance could be found in the juvenile crucian carp. Performance trade-off was detectable between aerobic metabolic capacity and anaerobic metabolic capacity in this species.