Archer fish jumping prey capture: kinematics and hydrodynamics

Abstract

Smallscale archer fish, Toxotes microlepis, are best known for spitting jets of water to capture prey, but also hunt by jumping out of the water to heights of up to 2.5 body lengths. In this study, high-speed imaging and particle image velocimetry were used to characterize the kinematics and hydrodynamics of this jumping behavior. Jumping used a set of kinematics distinct from those of in-water feeding strikes and was segmented into three phases: (1) hovering to sight prey at the surface, (2) rapid upward thrust production and (3) gliding to the prey once out of the water. The number of propulsive tail strokes positively correlated with the height of the bait, as did the peak body velocity observed during a jump. During the gliding stage, the fish traveled ballistically; the kinetic energy when the fish left the water balanced with the change in potential energy from water exit to the maximum jump height. The ballistic estimate of the mechanical energy required to jump was comparable with the estimated mechanical energy requirements of spitting a jet with sufficient momentum to down prey and subsequently pursuing the prey in water. Particle image velocimetry showed that, in addition to the caudal fin, the wakes of the anal, pectoral and dorsal fins were of nontrivial strength, especially at the onset of thrust production. During jump initiation, these fins were used to produce as much vertical acceleration as possible given the spatial constraint of starting directly at the water's surface to aim.

Presence of an audience and consistent interindividual differences affect archerfish shooting behaviour

“…While jumping may reduce the threat of kleptoparasitism, it only works for prey that are close to the water surface as archerfish are unable to jump as high as they can effectively shoot (Shih, Mendelson, & Techet, 2017). In situations where an archerfish must shoot, nearby conspecifics are likely to affect the decision making of the shooting fish.…”

Jumping dynamics of aquatic animals

“…Looking at animals larger than the capillary length scale, a small fish like the Trinidadian guppy can jump around 3.5 body lengths [7]. A detailed analysis of the archerfish kinematics show they can jump around 2.5 body lengths [29]. While the caudal fin appears to produce the most thrust, this study also showed the importance of the anal, pectoral and dorsal fins during thrust production using particle image velocimetry.…”

Hunting in archerfish – an ecological perspective on a remarkable combination of skills

“…Rossel et al, 2002;Reinel and Schuster, 2018a). Jumping, per se, is more costly and can be used only at low target height, but it can secure prey with no further investment needed and at overall costs that are comparable to shooting plus subsequent retrieval (Shih et al, 2017). When jumping, the fish position themselves directly below their prey (e.g.…”

“…When jumping, the fish position themselves directly below their prey (e.g. Shih et al, 2017), but when shooting, they take more lateral positions (e.g. Timmermans, 2001;Rossel et al, 2002;Schuster et al, 2004).…”