Archerfish Hunting Using Water Jet – Black Lagoon – Smithsonian Institution (2015)

The Archerfish posseses one of the most complex feeding behavior among fishes. Complex feeding behaviors involving proto-tool use are common among marine fishes. Scientists have noticed such behavior in many wrasses, in black spotted tuskfish, (Choerodon schoenleinii) from the Great Barrier Reef; in yellowhead wrasses (Halichoeres garnoti) off the coast of Florida; and in a sixbar wrasse (Thalassoma hardwicke) in an aquarium setting. For instance, wrasses crunch sea urchins against corals and use anvils to smash food into more gulpable pieces. Anecdotal evidence for the use of tools in marine fishes is abundant but documentation in the wild is rare.

The black spotted tuskfish uses jets of water for moving sand in order to dig clams out. Similarly the archerfish (Toxotes) uses water as a force. Impressively, the jet of water leaves the water interface and becomes a hunting projectile. The archerfish live in brackish waters of estuaries, mangroves and streams from India to the Philippines, Australia and Polynesia. Their eyes have evolved to maximize stereovision. They are widely spaced, large and mobile. Their vision can also compensate for the optical distortion produced by the refraction of light during water-to-air transition.

Their jaws and mouth structures are highly modified. A groove in the upper jaw allows squirting a beam of water by positioning their tongue against it. A fast compression of the throat and mouth forces the water through the groove like a squirt gun. Experienced fishes can accurately hit a target from a meter away (3 feet).

If you take your time to observe the fish, you will notice that most of the time they forage just like other fishes do. If the prey is close to the surface of the water, they may just leap to snatch. The water gun trick is optional.

The squirting behavior is quite adjustable depending on the type of prey which can be arthropods (insects and spider). Prey could even be rather large like juvenile inexperienced lizards. Size, weight, moving speed and grasping power of the prey determines whether a fish requires squirting of water in a single shot or in a sustained beam. Fishes may even learn to aim to shoot just under their prey on a surface to create a vectoral push to make it fall down into the water. This prevents the risk of prey escaping or being eaten by a rival fish.

Perhaps the most striking is the strategy deployed for flying prey. Depending on the speed and altitude of flying prey the fish exercises a “predictive leading strategy”. An archerfish brain can calculate the trajectory of the jet of water to account for the speed of a flying insect. Thus the fish aims ahead of the flying insect. If the insect is flying low, “turn and shoot” strategy is employed. The fish squirts while rotating its body horizontally to match the lateral movement of the target. In this way, the jet of water sweeps the trajectory of the insect increasing the probability of interception.

Archerfish are highly social. Research has shown that they have a fantastic capacity to observe and learn from each other. The hunting behavior is not innate but learned. Researchers in Germany studying archerfish in captivity at the Friedrich-Alexander University of Erlangen-Nürnberg observed that inexperienced individuals improved after watching many hundreds of attempts from both successful and unsuccessful fishes. This type of learning is quite a significant cognitive capacity indicating “theory of mind”. The scientists concluded that archerfish can project the world from the viewpoint of another archerfish. This “perspective taking” behavior within theory of mind enables “distance learning”. nest making and sexual display dances in most birds are in this learning by watching category.

Can they recognize prey? Distinguishing between poisonous vs. yummy insects would be very cool.

 

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