Aim affects fin interactions and wake topology in jumping archer fish*

Archer fish jumping for aerial prey rapidly accelerate from a stationary aiming position below the free surface. Herein we investigate how this aiming behavior affects propulsion during an archer fish jump. Using high-speed imaging, we find that the angle between the body and the free surface at jump onset varies with target prey height. Through volumetric synthetic aperture particle image velocimetry, we find that this posture considerably influences the upward contributions of the fish's initial propulsive tailbeats. Furthermore, we show that the orientation of the body causes different modes of interaction between the anal and caudal fins. These interactions are also found to differ between when the body has minimal upward velocity (i.e., jump onset) and when the body has a greater instantaneous velocity at later times during the jump. We find strong agreement between the cumulative effects of multiple propulsive motions, measured through wake impulse, and the instantaneous ballistic velocity of the fish. Our results highlight how discrete tailbeats and multi-fin propulsive strategies enable accurate jumping from a spatially- and visually-constrained environment.