#archer fish

We're shooting into a ballistic Wet Beast Wednesday with the archerfish. Lots of fish hunt insects, but not many fish can say they've mastered ranged combat. The archerfish is not most fish. These little longbowmen have some very cool adaptations that allow them to spit water in streams so accurate they can knock bugs out of the air.

(Image: a banded archerfish (Toxotes jaculatrix). It is a narrow, silvery fish with a pointed head and somewhat arrow-shaped body. The dorsal and anal fins are located far back on the body and are large. The eye is large for a fish of its size. Five black blotches run down the side. another out-of-focus archerfish is in the background. End ID)

Archerfish are 10 species in the genus Toxotes, which is the only genus in the family Toxotidae. They are silvery, laterally compressed (narrow) fish with black bands on the body that vary in shape based on species. The face is very pointed and the lower jaw protrudes beyond the upper jaw. The dorsal and anal fins are roughly the same size and sit far back on the body. Archerfish vary in size depending on species, but the largest can grow up to 30 cm (12 in), with the average being 10 cm (4 in). Archerfish have large and highly-developed eyes that face forward, giving them binocular vision. When targeting prey, the archerfish rotates its eyes so the image of the target appears in front and sides of the eye. The adaptations that allow archerfish to shoot down their prey involve both physiology and behavior. The roof of the mouth has a groove in it and the tongue can curl, resulting in a channel through the mouth. When shooting, the archerfish will from the channel, then force water through it by slamming its gill covers shut. This results in a stream of water that the fish can aim using its lower jaw.

(Gif: a shot of an archerfish spitting and knocking an insect off of a plant stem and into the water. End ID)

Archerfish are freshwater fish that live in rivers, streams, swamps, and ponds. Most species are fully freshwater, but some can tolerate brackish estuaries and mangrove swamps. Archerfish school in hunting parties of four or five and cooperate to shoot down prey. They swim near the surface of the water while looking for prey. Their targets are insects and spiders either flying over the water or resting on leaves, sticks, or other overhanging structures. Some of the largest species can hunt small lizards. When prey is sighted, the fish lines itself up with just the tip of the mouth out of the water and aims. Multiple fish will shoot at the same target to increase the odds of hitting it. The fish will persistently shoot at he target until it is hit or escapes. Once the target is hit and falls into the water, all the fish in the school will compete to catch it. Tests have shown that the fish can predict where falling prey will hit the water within 100 milliseconds of landing a shot. Adults can hit a target up to 3 meters (10 ft) away, but accuracy drops off after about half that distance. Archerfish can also catch insects via jumping instead of shooting if the target is low enough. Because the fish shape and use the water in new ways, they are considered one of the few animals (and even fewer fish) that both make and use tools.

(Image: an archerfish at the surface of the water. The tip of its mouth is above the water and a stream of water is being spat out. End ID)

What makes the shooting behavior even more interesting is that it is learned. Juvenile archerfish need to practice targeting and determining where food will fall. Among the problems they need to learn to compensate for is the effects of refraction between water and air as the fish don't expose their eyes to the air when hunting. Impressively, they can learn better technique by watching a more experienced archerfish hunting. This indicates that the fish can visualize the angles and vectors used by other fish and apply that to their own actions. Other skills archerfish have to learn is how much to spit to optimize their effort to the size of the target and how much they need to lead a moving target. The water they spit moves slower at the front of the stream, resulting in it becoming a big blob that can better stick to a bug and drag it down. The amount of force needed to get the best result is another thing that archerfish need to learn. Archerfish in captivity have also been shown to alter their behavior. For example, archerfish will stop targeting flies glued to substrate once they realize the flies won't wall into the water, but can be trained to spit at non-food objects if they are rewarded with food afterwards. The ability of archerfish to rapidly learn complex new behaviors makes them of special interest to scientists studying neurology, cognitive science, and animal behaviorism. Archerfish have also recently been seen to shoot while underwater to uncover food buried in silt.

(Image: an archerfish spitting at a fly on a leaf overhanging the water, as seen from above. End ID)

Aside from their shooting and learning behavior, not much has been studied about archerfish behavior. We do know they swim upstream to mate and lay eggs. Once the eggs hatch, the fry will be carried downstream and mature. They feed on zooplankton and algae until reaching about 2.5 cm (1 in) in length, at which point they begin practicing spitting. Young archerfish live in larger schools that use sheer force of numbers to compensate for their worse accuracy. As they grow larger and get more skilled at sharpshooting, the fish will split off into smaller hunting parties.

(Image: a close up shot of an archerfish's face as it spits. End ID)

Not much is known about archerfish conservation needs, though they are abundant in their habitats. Pollution and habitat loss are the largest threats to them. Archerfish are kept in captivity as aquarium fish, though they are not recommended for inexperienced aquarists as they have some specialized care needs. They prefer live prey to fish food and rarely breed in captivity.

Archerfish!