A fast fish swimming protocol that provides similar insights to critical swimming speed.

Performance measures are an important tool to assess the impact of environmental change on animals. In fish, performance is often measured as critical swimming speed (Ucrit), which reflects individual maximal physiological capacities. A drawback of Ucrit is that trials are relatively long (∼30-75 min). Ucrit may therefore not be suitable for several repeated measurements because of the potential for training effects, long recovery periods, and low throughput. Here we test a shorter (∼4-5 min) protocol, "Ucrit fast" (UCfast) in zebrafish (Danio rerio). We show that UCfast and Ucrit have similar, significant repeatabilities within individuals. Unlike Ucrit, repeated UCfast trials did not elicit a training effect. Both UCfast and Ucrit provide the same insights into thermal acclimation, and both provide similar estimates of individual acclimation capacity in doubly acclimated fish. We propose that UCfast is a valid substitute for Ucrit particularly when higher throughput and several repeated measures are necessary.