Swimming ability and behavior of Mrigal carp Cirrhinus mrigala and application to fishway design

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.