Gait transition speed as an alternate measure of maximum aerobic capacity in fishes
This study demonstrated that the transition from a steady to an unsteady locomotory gait (USTmax) in juvenile brook trout Salvelinus fontinalis can be measured easily using a new tilting raceway design and a simple experimental protocol. It was found that USTmax increased linearly with fork length (LF), and that this relationship was statistically identical in fish that swam volitionally in the raceway and those that were forced to perform, although slightly different data processing methods were needed in the latter to achieve this result. Furthermore, the relationship between LF and USTmax was statistically identical to that between LF and critical swimming speed (Ucrit), although LF in the former relationship explained 83% of the variance compared to 37% in the latter. This finding indicates that gait transition speed can be used to estimate maximum aerobic capacity, with less unexplainable variance than Ucrit. Gait transition speeds were also determined from Ucrit tests; however, this required measuring and incorporating ground speed into the analysis. USTmax as determined in the Ucrit tests was not significantly different from that measured in the raceway, suggesting that gait transition speed can be measured in raceways or swim tunnel respirometers.