Critical swimming speed (Ucrit) scaled with mass with an exponent of 0.29 (‘CI-95%: 0.07–0.51). Ucrit is a complex performance trait that involves an aerobic and an anaerobic component. Whereas aerobic energy production by red muscle tissue is predominant at slow speeds, it is gradually complemented by anaerobic metabolism by white muscle at higher speeds. These two components of Ucrit do not scale in a similar fashion with body mass as aerobic swimming is more affected by body size than anaerobic swimming (Goolish, 1991). Moreover, anaerobic metabolism contributes a greater proportion of energy requirements to high-speed swimming in large fish than in small fish (Goolish, 1991; Clark et al., 2012). Whether these elements contribute to the observed scaling exponent remains elusive considering our relatively narrow size range. Future research will investigate the allometry of the relative contribution of aerobic and anaerobic metabolism to swimming performance.