The effect of substratum type on aspects of swimming performance and behaviour in shortnose sturgeon Acipenser brevirostrum.

The swimming performance and associated swimming behaviour (i.e. substratum-skimming, station-holding and free swimming) were assessed in shortnose sturgeon Acipenser brevirostrum during critical swimming and endurance swimming tests over a rough and a smooth substratum. It was hypothesized that the addition of a rough substratum in the swimming flume may provide a surface for the A. brevirostrum to grip and offer an energetic advantage. Substratum type did not affect the critical swimming performance, but A. brevirostrum consistently performed more bottom behaviours (i.e. substratum-skimming and station-holding) while on a smooth substratum. Acipenser brevirostrum had little contact with the rough substratum until the velocity was >1 body length s(-1) . Endurance swimming time was significantly lower for A. brevirostrum over the rough bottom at the highest velocity (30 cm s(-1) ) which may be attributed to the observed increase in free swimming and decrease in bottom behaviours. During endurance swimming, the rough substratum was mainly used at intermediate velocities, suggesting that there may be a stability cost associated with being in contact with the rough substratum at certain velocities.