Repeatability of burst swimming performance in medaka (Oryzias latipes).

Burst swimming performance (U) is a putative indicator of "success" in wild fish. In this study, thirty-five lab-reared medaka (Oryzias latipes) were tested for U using a French press exercise system. Fish were tested once a week for four consecutive weeks and repeatability was estimated in several ways to allow comparisons between studies. Following the initial swimming tests, 50% of fish were either thermally stressed, or not, for 180 s prior to testing U once a week for four consecutive weeks. Burst swimming performance was found to be 24.0 ± 6.7 (s.d.) cm s and repeatability prior to the thermal stress experiment was estimated to be 0.28 (intraclass correlation coefficient) with an upper and lower limit of 0.48 and 0.12, respectively. The measured U and repeatability estimate in the thermal stressor experiment did not significantly differ from the first four trials. Swimming velocities observed match what is known about medaka swimming capabilities and, interestingly, are similar to maximum current velocities observed in their native habitat. Furthermore, our repeatability estimates confirm that burst swimming performance in medaka is a repeatable trait and validate the apparatus and swimming test used.