A comparison of two methods for estimating critical swimming speed (U-crit) in larval fathead minnows: the laminar flow assay and the spinning task assay

Critical swimming speed (U-crit) is considered a good predictor of swimming capabilities in fish. To estimate U-crit, a fish is exposed to an incrementally increasing laminar flow of water until it cannot maintain its position against the current. The spinning task assay has been proposed as an alternative method to traditional laminar flow methods; however, these methods have not been directly compared. Thus, the goal of this study was to determine whether the spinning task assay is a suitable alternative to traditional laminar flow assays. To that end, the performance of fathead minnows in each assay was compared at three time points (14, 19 and 24 days post-fertilization, dpf). In 14 dpf fish, U-crit estimates were similar regardless of the assay used. However, at 19 and 24 dpf, U-crit estimates derived from the two assay types were significantly different. This indicates that the assays are not equivalent to one another and that the spinning task assay is not a suitable alternative to the laminar flow assay for the determination of U-crit.