Abstract: Bighead carp (Aristichthys nobilis) is an important commercial fish in China. Sustained and prolonged swimming speeds are two important parameters to assess the swimming performance of the fish. In this study, one hundred and eighteen juvenile bighead carp were divided into three groups according to total length (TL): 12.5-17.5, 17.5-22.5 and 22.5-27.5 cm. Fixed velocity tests were used to measure sustained and prolonged swimming speeds in an open channel flume. Sustained swimming speeds for the three groups were 13.7-39.8, 46.1-78.0 and 60.3-75.7 cm·s^-1, and prolonged swimming speeds were 29.9-60.0, 65.3-120.2 and 59.2-122.9 cm·s^-1, respectively. Nearly all (>98%) of the fatigue time was in one of two ranges: either <10 min or >200 min. Both sustained swimming speed (U_s) and prolonged swimming speed (U_p) increased as a linear function of water temperature (T) from 18 ℃ to 26.3 ℃. The correlations were significant if absolute speeds were converted to relative speeds (U/TL, TL is the total length): U_s=0.19T-1.57 (n=27, R²=0.48, P<0.001); U_p=0.20T-0.63 (n=83, R²=0.22, P<0.001). The results indicate that the time interval needs to exceed 10 min in the critical swimming speed (U_crit) test, and the penultimate velocity before fatigue can be considered the maximum sustainable speed. Temperature also significantly affected the sustained and prolonged swimming speeds, displaying the same trend as U_crit in the optimal temperature range.

Key words: Changzhou Dam, fishway, passage efficiency.