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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.

Fish swimming behavior is important for their survival. Burst swimming, prolonged swimming, and their effect on each other were examined for Gymnocypris potanini firmispinatus. Test fish were randomly assigned to two groups, one group was tested for critical swimming speed (Ucrit), and the other was tested for burst speed (Uburst). After a 30-min recovery period, both groups were subjected to Uburst testing. The Uburst value measured following the Ucrit test was termed Uburst-c and Uburst-b was measured following the initial Uburst test. Results include two primary findings. (1) There were significant differences between Uburst and Uburst-c, and between Uburst and Uburst-b, indicating that the effect of fatigue from both prolonged and burst swimming on subsequent burst swimming performance is significant. (2) The recovery ratio after fatigue resulting from prolonged swimming was significantly lower than the recovery ratio after fatigue resulting from burst swimming. The differences between Uburst-c and Uburst-b was not significant. Therefore, whether or not prolonged swimming leads to deeper fatigue than burst swimming will require additional research. The findings from this study on prolonged and burst swimming and their effects on subsequent burst swimming will support continued improvement of fishway design.

The objective of this research was to determine the effects of diel cycle and flow velocity on rheotaxis, measure the swimming performance of Perch-barbel (Percocypris pingi, Tchang, 1930) and use the results to recommend an appropriate fishway entrance velocity and fish lift operating schedule. PIT tagging was used to monitor fish rheotaxis for 48 h in four channels with differing flow characteristics. Swimming performance tests were conducted in a swimming respirometer and induced flow speed, critical swimming speed and critical burst speed were determined. The relationship between flow velocity and fish swimming behavior was analyzed to determine the optimal attraction flow velocity. There were three primary findings. (1) Test fish were active both day and night, but made more attempts, had longer retention times, and swam longer through-water distances in all channels during the day. (2) Entry, retention, and effort were maximum at a flow velocity of 0.2 m/s (26% of absolute critical swimming speed (m/s) and 29% of relative critical swimming speed (bl/s)). (3) Attempt number, retention time and through-water distance increased with body length in the channel with greatest activity. Collectively, these data suggest that passage of P. pingi will be optimized by fishways operating throughout the day and most of the night, although these conditions could lead to size-based selectivity in passage.

Anaerobic metabolism begins before fish reach their critical swimming speed. Anaerobic metabolism affects the swimming ability of fish, which is not conducive to their upward tracking. The initiation of anaerobic metabolism therefore provides a better predictor of flow barriers than critical swimming speed. To estimate the anaerobic element of metabolism for swimming fish, the respiratory metabolism and swimming performance of adult crucian carp (Carassius auratus, mass = 260.10 ± 7.93, body length = 19.32 ± 0.24) were tested in a closed tank at 20 ± 1 °C. The swimming behavior and rate of oxygen consumption of these carp were recorded at various swimming speeds. Results indicate (1) The critical swimming speed of the crucian carp was 0.85 ± 0.032 m/s (4.40 ± 0.16 BL/s). (2) When a power function was fitted to the data, oxygen consumption, as a function of swimming speed, was determined to be AMR = 131.24 + 461.26Us1.27 (R2 = 0.948, p &lt, 0.001) and the power value (1.27) of Us indicated high swimming efficiency. (3) Increased swimming speed led to increases in the tail beat frequency. (4) Swimming costs were calculated via rate of oxygen consumption and hydrodynamic modeling. Then, the drag coefficient of the crucian carp during swimming was calibrated (0.126–0.140), and the velocity at which anaerobic metabolism was initiated was estimated (0.52 m/s), via the new method described herein. This study adds to our understanding of the metabolic patterns of fish at different swimming speeds.

To mitigate the impact of river fragmentation on fish resulting from dams, specifically the fragmentation of Indian rivers, the design and construction of high-efficiency fishways is important. Information on fish swimming ability and behavior is necessary to develop design criteria for the target species, Cirrhinus mrigala, a cyprinid native to India, Pakistan and Bangladesh. Swimming ability and behavior data for the genus are limited. To augment existing information, the swimming ability and behavior of juvenile C. mrigala were investigated by determining their induced flow velocity (Uind), critical swimming speed (Ucrit), and burst speed (Uburst) in a swimming respirometer. To facilitate application to fishway design, swimming assessment data were converted to a cumulative response; for Uind, it is the cumulative percentage of fish swimming against the current at a given velocity, and for Ucrit and Uburst, it is the percentage of fish able to maintain a given velocity for the specified time interval without fatigue. Results include 2 primary findings. (1) The cumulative response velocity (%) of fish induced to swim, or reach fatigue, increased with flow velocity. The cumulative velocity is useful for developing fishway design criteria. (2) The mean values of Uind, Ucrit, and Uburst were 0.427 ± 0.013, 2.768 ± 0.146 and 3.493 ± 0.121 body lengths s-1 (±SE). The values of Ucrit and Uburst indicate that the swimming ability of C. mrigala is relatively low for a cyprinid.

The bighead carp (Hypophthalmichthys nobilis) is one of the most commercially important freshwater fish species in China, but their abundance has declined considerably in recent decades, partly due to river regulation. In other countries it is invasive, posing an ecological and economic threat. To improve fish pass effectiveness at impediments to migration in its native range, and create velocity barriers to reduce range expansion where it is invasive, an improved understanding of swimming ability and behaviour is needed. The burst, prolonged, and sustained swimming performance of juvenile bighead carp were quantified experimentally through constant acceleration trials (Umax), fixed velocity tests, and volitional passage efficiency trials through three consecutive constrictions. The effects of fork length (FL), temperature, swimming speed and method (swim chamber/open channel flume section) on endurance in fixed velocity trials were evaluated. The utilisation of low velocity areas close to the flume edge and floor at different mid-channel velocities was also explored. The mean sustained swimming speed in endurance tests was 3.84 FL s?1 (range equivalent to 0.37–0.78 m s?1), and burst speeds reached 12.78 FL s?1 (up to 1.22 m s?1 for larger fish). The meanUmax was 6.81 FL s ?1 (0.51 m s?1). In fixed velocity trials, method did not influence endurance and fish rarely utilised low velocity areas in the corners of the flume when water velocity exceeded sustained swimming ability. Passage efficiency decreased at successive flume constrictions, possibly indicating a poor repeat burst swimming performance. Field validation is required to verify wild bighead carp behaviour and passage in the hydraulic conditions created by fish passes.