The trade-off between steady and unsteady swimming performance in six cyprinids at two temperatures

Abstract

The purpose of this study was to investigate whether a functional trade-off (as assessed by a negative phenotypic relationship) between steady and unsteady swimming performance exists in six selected cyprinids and whether the possible trade-off changed with temperature. We measured the critical swimming speed (Ucrit, i.e., the water speed at which a fish can no longer maintain its position or its maximum sustainable swimming speed), metabolic rate (ṀO2) and fast-start performance in juvenile grass carp (Ctenopharyngodon idellus), crucian carp (Carassius auratus), qingbo (Spinibarbus sinensis), Chinese bream (Parabramis pekinensis), common carp (Cyprinus carpio) and sharp-jaw barbel (Onychostoma sima) at 15 and 25°C. Steady swimming performance as indicated by Ucrit and unsteady swimming performance as indicated by maximum linear velocity (Vmax), maximum linear acceleration (Amax) and the escape distance during 120ms (S120ms) varied significantly among species and between temperatures (P<0.05). There was no significant relationship between steady and unsteady swimming performance at low temperature. Ucrit was positively related to Vmax at 25°C. These findings clearly demonstrated that the relationship between steady and unsteady swimming performance changed with temperature. Both steady and unsteady swimming performance increased significantly with temperature. However, the thermal sensitivity of Ucrit was negatively related to that of the fast-start variables. This result suggested that a trade-off exists in the temperature reaction norm of the two types of swimming performance among the six cyprinids.