Migration barriers and resulting habitat fragmentation are a major conservationconcern for freshwater fishes. Characterizing the swimming abilities of fish is vital forfishway design and identifying potential movement barriers. The objective of this studywas to assess the swimming performance of two of the most widely distributed prairiefishes, the large-bodied, large river sauger Sander Canadensis, and the small-bodied,small stream longnose dace Rhinichthys cataractae. Swimming performance for bothspecies was assessed using a variety of metrics (passage success, maximum ascentdistance, maximum sprint speed) in an open channel flume over a range of velocities(sauger, 51, 80, 93 cm/; dace, 39, 64, 78, and 90 cm/s), temperatures (sauger, 10.0, 14.3,18.3°C; dace, 10.7, 15.3, and 19.3°C ) , and body sizes (sauger, 34.0-43.9 cm; dace, 4.6-12.4 cm). Passage success of sauger was surprisingly high (91%) over all test velocities,as was the mean maximum sprint velocity (mean, 219 cm/s). Contrary to expectations,water temperature and body size had little effect on swimming performance. Videoobservation showed that sauger transitioned from steady sustained swimming (aerobicmetabolism) to unsteady, burst-glide or steady burst swimming (anaerobic metabolism) at97 cm/s. Additional testing of sustained time of burst swimming by sauger in a swimtunnel (critical velocity, Usprint) showed they are capable of short term maximum bursts of124 cm/s over a 15 second duration before fatigue. Longnose dace had high passagesuccess in the test flume (95%) at test velocities of 39 and 64 cm/s, but success ratedropped markedly at higher velocities (66% at 78 cm/s and 19.7% at 90 cm/s). Daceswam along the bottom of the flume at all test velocities, but increased position-holdingas velocity increased. Their maximum sprint velocity (139 cm/s) was about half that ofsauger. Dace swimming performance generally increased with water temperature andbody size.
