Kinematics and mechanics of fast-starts of rainbow trout Oncorhynchus mykiss and northern pike Esox lucius
Creators: name: Harper, David Gordon
Publisher: name: University of British Columbia
Year: 2011

description: Film is commonly used to estimate the fast-start performance of fish. An analysis of hypothetical, film-derived, and accelerometer-measured acceleration-time data of fish fast-starts indicates that the total error in film studies is the sum of the sampling frequency error (i.e., the error due to over-smoothing at low film speeds) and measurement error. The error in film based studies on the acceleration performance of fish is estimated to be about 33 to 100% of the maximum acceleration, suggesting that other methods of estimating acceleration should be employed. The escape performance of rainbow trout Oncorhynchus mykiss and northern pike Esox lucius (mean lengths 0.32 m and 0.38 m, respectively) were measured here with subcutaneously implanted accelerometers. Acceleration-time plots reveal two types of escape fast-starts for trout and three for pike. Simultaneous high-speed ciné films demonstrate a kinematic basis for these differences. Trout performing C-shaped fast-starts produce a unimodal acceleration-time plot (type I), while during S-shaped fast-starts a bimodal acceleration-time plot (type II) results. Pike also exhibit similar type I and II fast-starts, but also execute a second S-shaped fast-start that does not involve a net change of direction. This is characterized by a trimodal acceleration-time plot (type III). Intraspecific and interspecific comparisons of displacement, time, mean and maximum velocity, and mean and maximum acceleration rate indicate that fast-start performance is significantly higher for pike than for trout, for all performance parameters. This indicates that performance is related to body form. Overall mean maximum acceleration rates for pike were 120.2 ± 20 m s⁻² (x ± 2S.E.) and 59.7 ± 8.3 m s⁻² for trout. Performance values directly measured from the accelerometers exceed those previously reported. Maximum acceleration rates for single events reach 97.8 m s⁻² and 244.9 m s⁻² for trout and pike, respectively. Maximum final velocities of 7.06 m s⁻¹ (18.95 L s⁻¹, where L is body length) were observed for pike and 4.19 m s⁻¹ (13.09 L s⁻¹) for trout; overall mean maximum velocities were 2.77 m s⁻¹ for trout and 3.97 m s⁻¹ for pike. The fast-start performance of pike during prey capture was also measured with subcutaneously implanted accelerometers. Acceleration-time plots and simultaneous high-speed cin6 films reveal four behaviours with characteristic kinematics and mechanics. As for the escape data, fast-start types are identified by the number of large peaks that appear in the acceleration-time and velocity-time data. Comparisons of mean performance were made between each type of feeding fast-start. Type I fast-starts were of significantly (i.e., p &lt; 0.05) shorter duration (0.084 s) and displacement (0.132 m) than type III (0.148 s and 0.235 m) and type IV (0.189 s and 0.307 m) behaviours, and higher mean and maximum acceleration (38.6 and 130.3 m s⁻², respectively) than the type II (26.6 and 95.8 m s⁻²), type III (22.0 and 91.2 m s⁻²), and type IV (18.0 and 66.6 m s⁻²) behaviours. The type II behaviours were also of shorter duration and displacement, and of higher mean acceleration than type IV fast-starts, and were of significantly shorter duration than the type LU behaviours. Prey capture performance was compared to escapes by the same individuals. When data are combined, regardless of mechanical type, mean acceleration (37.6 versus 25.5 m s⁻²), maximum acceleration (120.2 versus 95.9 m s⁻²), mean velocity (1.90 versus 1.57 m s⁻¹), and maximum velocity (3.97 versus 3.09 m s⁻¹) were larger, and duration shorter (0.108 versus 0.133 s) during escapes than during prey capture. No differences were found through independent comparisons of the performance of feeding and escape types II and III, but type I escapes had significantly higher mean velocity (2.27 versus 1.58 m s⁻¹), maximum velocity (4.70 versus 3.12 m s⁻¹), and mean acceleration (54.7 versus 38.6 m s⁻²) than the type I feeding behaviours. Prey capture performance was also related to prey size, apparent prey size (defined as the angular size of the prey on the pike's retina), and strike distance (the distance from the pike to the prey at the onset of the fast-start). Mean and maximum acceleration increased with apparent size and decreased with strike distance, while the duration of the event increased with strike distance and decreased with apparent size. No relation was found between the actual prey size and any performance parameter. Strike distance ranged from 0.087 to 0.439 m, and decreased as the apparent size increased from 2.6 to 9.9° (r² = 0.75). The type I behaviour was usually employed when the strike distance was small and the prey appeared large. As strike distance increased and apparent size decreased, there was a progressive selection of type II, then III, then IV behaviours.