A fast fish swimming protocol that provides similar insights as critical sustained 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 sustained swimming speed (U crit ), which reflects individual physiological capacities. A drawback of U crit is that trials are relatively long (∼30-75 min). U crit is therefore not suitable for repeated measurements because of the potential for training effects, long recovery periods, and low throughput. Here we test a shorter (∼4-5 min) protocol, “U crit fast” (U Cfast ) in zebrafish ( Danio rerio ). We show that U Cfast and U crit have similar, significant repeatabilities within individuals. Unlike U crit , repeated U Cfast trials do not elicit a training effect. Both U Cfast and U crit provide the same insights into thermal acclimation, and both provide similar estimates of individual acclimation capacity in doubly acclimated fish. We propose that U Cfast is a valid substitute for U crit particularly when higher throughput and repeated measures are necessary.