Linking behaviour and performance: intermittent locomotion in a climbing fish

How locomotory performance is influenced by prior experience and behaviour is of adaptive significance. The relationship between kinematics, behaviour and performance was investigated by assessing a previously undescribed mode of climbing locomotion performed by adult Pacific lamprey. The lampreys were challenged with a 1.4 m vertical weir under an experimental setting. The majority of ascents used intermittent bouts of climbing (on an average approximately one-fifth of total ascent time) via powerful cycles of axial undulation at 0.35-1.25 Hz, interspersed with periods of stationary attachment with the oral disk. However, two of the most rapid ascents (57 and 85 s) occurred during one continuous bout at a low cycle frequency (c. 0.38 and 0.50 Hz). Probability of success and ascent time was positively related to experience climbing the weir. The ratio of time spent actively climbing to time spent resting decreased with distance travelled, indicating fatigue. Ascents with long periods of activity had correspondingly high durations of recovery. Moreover, time to ascend was positively related to the proportion of time spent stationary in ascents that took < 300 s. The findings suggest that modification of intermittent locomotion allows Pacific lamprey to compensate for variation in climbing performance and can extend distance travelled before exhaustion.