The Swimming Performances of Individual Largemouth Bass (Micropterus Salmoides) Are Repeatable

Abstract

Previous studies have shown that the critical swimming speed (Ucrit) of largemouth bass, Micropterussalmoides Lacepede, is significantly influenced by a number of factors including body mass'(Beamish, 1970), training (Farlinger and Beamish, 1978), water temperature (Hocutt, 1973;Kolok, 1991)and photoperiod (Kolok, 1991).These studies share a common approach in that they were primarily concerned with comparing mean values of Ucritof fish from different treatment groups, and individual variation within the groups was treated as statistical noise. While this approach is valid, it may overlook a significant source of performance variation - the variation found among individuals. Recent research (for a review, see Bennett, 1987)into the locomotor performance of amphibians and reptiles has suggested that individual variation is substantial and repeatable (i.e. performance variation of an individual forced to perform multiple times will be minor compared to the variation found when a number of individuals are forced to perform once). This research has been conducted on animals at a constant temperature, and also before and after an acute temperature change. No study has been done to determine whether performance repeatability is maintained following a chronic change in temperature. This may be particularly important with respect to fishes because many fish undergo physiological and morphological changes when subjected to chronic changes in water temperature. In the current study, variations in the Ucritof individual bass were quantified, and performance repeatability was established at 11 and 22°C and after an acute and chronic decrease in water temperature from 20 to 100c. Juvenile largemouth bass were obtained from the Wray Fish Hatchery, Colorado Division of Wildlife, during November and August. The fish used during November (N=7) varied from 7.8 to 9.8cm (mean 9.0cm) in fork length and from