Repeat swimming performance of mature sockeye salmon following a brief recovery period: a proposed measure of fish health and water quality

Measurements of swimming ability, such as critical swimming speed (Ucrit), have commonly been used as indicators of the effects of environmental challenges on the general health of fish. In this study, we introduce repeat swimming performance as a particularly sensitive means to assess fish health and the effects of environmental stressors. Adult sockeye salmon (Oncorhynchus nerka) performed two Ucrit tests separated by a 40-min recovery period. When recovery ability was expressed as a ratio of Ucrit values in the first and second swim challenges (Ucrit,2/Ucrit,1), control fish exhibited recovery ratios of unity (0.98 ± 0.01 (mean ± SEM)). In contrast, the recovery of fish pre-exposed to between 0.12 and 0.77 mg·L-1 dehydroabietic acid (DHA) for 8-14 h, and swimming in either hypoxia or normoxia, was impaired. These fish had recovery ratios significantly lower than unity (0.92 ± 0.02) despite swimming to a similar initial Ucrit as control fish. The effect of pre-exposure to DHA was also evident in measure...