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The primary objective of this investigation was to study the effect of altitude on fish swimming ability. Different species were tested to ensure that the differences observed are not associated with a single species. Fish critical swimming speed and burst speed were determined using stepped-velocity tests in a Brett-type swimming respirometer. Based on the effects of water temperature and dissolved oxygen, it is clear that the swimming ability of fish decreases as altitude increases. Further, because the effects of high altitude on fish physiology go beyond the effects of lower temperature and dissolved oxygen, we recommend that fish swimming ability be tested at an altitude similar to the target fishway site to ensure the validity of fish data used for fishway design.

Schizothorax oconnori Lloyd is a local endemic species, one of the most frequently observed species in the Tibet plateau, China, and the representative species of cold-water fish in the Yarlung Zangbo River basin. Knowing the flow velocity preference of fish is essential for understanding the mechanics of their locomotion, and part of the biological foundation required for habitat restoration. The flow velocity preference of Schizothorax oconnori swimming upstream was investigated using a four-channel flume. The flow fields in each channel were nearly uniform, but the flow velocity varied by channel. Test fish swam upstream, of their own volition, into a channel and were recorded by PIT (Passive Integrated Transponder) antennas as they entered the channel. The proportion of fish entering each channel was recorded and changes in activity level during the experiment were analyzed to detect diurnal and nocturnal cycles of activity. The choice among channels made by the test fish differed significantly, indicating that Schizothorax oconnori display a preference for flow velocity. Furthermore, it was demonstrated that the preference for flow velocity varied by season, with a preference for relatively high velocity in late July and a relatively low velocity in late August. This variation in preference may be attributed primarily to different feeding strategies in the two seasons and to differing maximum flow velocities in the two experiments. Due to fatigue, or acclimation to the constant flow field, fish activity decreased significantly after 10 h. Schizothorax oconnori was more active at night than during the day, attributed to its benthic nature and the relatively high light level in the shallow flume. Based on our findings, we make the following recommendations for fish passage design: (1) The flow field should be non-uniform to accommodate a flow preference that varies with season, and which helps prevent fatigue; (2) Avoid excessively long fish passageways and provide a combination of water depth and shading that provides a satisfactory light level.

The swimming kinematics (how fish move) and dynamics (how forces effect movement) of Schizopygopsis malacanthus were investigated during the determination of Ucrit by stepped velocity testing. A video tracking program was used to record and analyze the motion of five test fish in a Brett-type flume during each velocity step. The findings fell into three groups: (1) Even when flow was uniform, fish did not swim steadily, with speeds fluctuating by 2.2% to 8.4% during steady swimming. The proportion of unsteady swimming time increased with water velocity, and defining steady and unsteady swimming statistically, in terms of the definition of standard deviation of instantaneous displacements, may have higher accuracy. (2) In steady swimming, the forward velocity and acceleration of fish were correlated with body length (p < 0.05), but in unsteady swimming the correlations were not significant. The maximum swimming speed (1.504 m/s) and acceleration (16.54 m/s2) occurred during unsteady swimming, but these measurements may not be definitive because of tank space constraints on fish movement and the passive behavior of the test fish with respect to acceleration. (3) Burst-coast swimming in still water, investigated by previous scholars as an energy conserving behavior, is not the same as the gait transition from steady to unsteady swimming in flowing water. In this study, the axial force of fish swimming in the unsteady mode was significantly higher (×1.2~1.6) than in the steady mode, as was the energy consumed (×1.27~3.33). Thus, gait transition increases, rather than decreases, energy consumption. Our characterization of the kinematics and dynamics of fish swimming provides important new information to consider when indices of swimming ability from controlled tank testing are applied to fish passage design.