Swimming capability and activity metabolism of subadult Schizothorax macropogon

Schizothorax macropogon (locally known as Huzi Yu), a fish species commonly found in Yaluzangbujiang River, has been declining quickly in recent years. Overfishing is one of the important factors. Hydropower projects that will be built on the river will lead to more significant decline in this species. Building fish passage incorporated into dams together with other fisheries management actions would help maintain local fish fisheries. The swimming capability within specific habitats is likely to be very important data that might be applied to the design of a fishway for S. macropogon. To obtain data that can be applied to the design of a fishway for S. macropogon and other species in the community, a laboratory study on the swimming capability and activity metabolism of wild subadult S. macropogon was conducted in a self-designed apparatus with a video camera system recording their swimming behavior at four acclimation temperature (5, 10, 15 and 18℃) to reflect seasonal water temperature. Specimens of wild S. macropogon body length (BL) ranging from 20-29 cm, body mass ranging from 176-324 g were selected and their critical swimming speed (Ucrit), oxygen consumption rate MO2, mgO2/(kgh), tail beat frequency (TBF, /min), and stride length (Ls, /beat) were measured and compared during steady swimming at varying flow rates. Both absolute critical swimming speeds (Ucrit-a, m/s) and relative critical swimming speeds (Ucrit-r, BL/s) of subadult S. macropogon increased with the temperature from 5℃ to 18℃ and the relation was approximately linearity (P0.001). The Ucrit-a were 0.880.07, 1.090.07, 1.240.15, 1.490.15 m/s and Ucrit-r were 3.960.21, 4.40.16, 4.90.18 and 5.350.14 BL/s respectively at four different temperatures. The maximum Ucrit did not appear during the temperature from 5℃ to 18℃. Power function models at four different temperatures well described the correlation between MO2 and swimming speed with high correlation coefficient (P0.05). The derived models showed that MO2 increased with the increase of swimming speed and the increase was more significant as the temperature was higher. The speed exponents of the power fit at four different temperatures were 2.4, 2.6, 2.8 and 3.1, which means the efficiency of aerobic swimming decreased with the increase of temperature and temperature had a significant effect on swimming performance in subadult S. macropogon. There was a significant positive linear correlation between TBF and swimming speed (P0.001) at natural water temperature (5-9℃) which was in accord with most reference data, but stride length (Ls) was only weakly correlated with swimming speed and showed three different stages. Recording analyses indicated that S. macropogon depended on caudal fin to generate forward thrust and employed three velocity-dependent swimming modes during the increase of swimming speed: a discontinuous stroke-and-glide swimming behavior at low velocity, a continuous swimming behavior as velocity increase and a discontinuous burst-and-glide swimming behavior at velocities near Ucrit. This has been shown to be an energy-saving swimming behavior and may benefit the fish by optimizing muscle fiber power output and efficiency. This investigation provided data on the swimming capability and energetics of wild subadult S. macropogon that would add to the basic science required for fishway design and contribute to the protection of this species.