Critical swimming speeds (mean ±s.e.) for juvenile shortnose sturgeon Acipenser brevirostrum were 34·4 cm s−1± 1·7 (2·18 ± 0·09 body lengths, BL s−1). Swimming challenges at 10, 20 and 30 cm s−1 revealed that juvenile A. brevirostrum are relatively poor swimmers, and that the fish did not significantly modify their swimming behaviour, although they spent more time substratum skimming (i.e. contact with flume floor) at 30 cm s−1 relative to 10 cm s−1. When present, these behavioural responses are probably related to morphological features, such as flattened rostrum, large pectoral fins, flattened body shape and heterocercal tail, and may be important to reduce the costs of swimming.