The Kinematics and Performance of the Escape Response in the Angelfish (pterophyllum Eimekei)

The kinematics of turning manoeuvres and the distance-time performance in escape responses of startled angelfish {Pterophyllum eimekei) are investigated employing high-speed cinematography (400Hz). All escape responses observed are C-type fast-starts, in which the fish assumes a C shape at the end of the initial body contraction (stage 1). Kinematic analysis of the subsequent stage (stage 2) allows the response to be classified into two types: single bend (SB), in which the tail does not recoil completely after the formation of the C, and double bend (DB), in which it does. The two types of response have different total escape angles (measured from the subsequent positions of the centre of mass, SB 120.0°; DB 73.3°, P<0.005), different stage 2 turning angles (in the same direction as stage 1 for SB, 11.0°; in the direction opposite to stage 1 for DB, -21.9°: P<0.0005) and different maximum angular velocities in the direction opposite to the initial one (SB -8.08 rads"; DB -56.62 rads": P<0.001). There are no significant differences in stage 1 kinematics for the two types of escape. Stage 1 turning angle is linearly correlated to stage 2 turning angle for DB only (P<0.01; 7^=0.60) and to total escape angle for both types of response (7<0.0001; ^=0.80). Stage 1 duration is linearly correlated to stage 1 turning angle (P<0.0001; r=0.83) and to total escape angle (P<0.0001; ^=0.72) for both types of escape.