Abstract: Predation stress (both duration and intensity of the stress) affects locomotor ability of fish. The escape strategies of prey fish are different when encountering predators. We investigated the responses of locomotor ability of the juvenile black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) (four major Chinese carps) to predation stress from snakehead fish (Channa Argus) and Southern catfish (Silurus meridionalis). The prey fish were subjected to predation stress under no-predation (control), low-predation (net-separated stress, i.e. indirect stress) and high-predation (direct stress), with three duration levels of 0, 7, and 14 d. The differences of locomotor ability among the four Chinese carps were compared, and the adaptability of steady and unsteady swimming ability under different levels of predation stress was investigated. The results showed that there was a trade-off between steady swimming and unsteady swimming for the four Chinese carps. In response to the predation stress, the fast-start swimming performance was mainly enhanced, whereas the critical swimming performance tended to decrease. The four Chinese carps all showed the C-type fast-start swimming pattern, with body rotation was mainly completed in stage 1 and the speed performance was maximized in stage 2 during the fast-start process. Under the predation pressure, there were interspecific differences in the escape strategies of the four Chinese carps. The main escape strategy of black carp and grass carp was to shorten the response latency, which showed stronger reduction with increasing predation intensity. Silver carp showed a significant reduction in response latency and an increase in escape angle under low predation stress, and an increase in escape velocity under high predation stress. Bighead carp adopted increasing escape velocity as the main response strategy after predation stress, and the response latency tended to decrease, but the response was not significant.

Key words: predation stress, critical swimming, fast-start, four major Chinese carps.