<P> Archerfish or spinnerfish bodies are deep and laterally compressed, with the dorsal fin, and the profile a straight line from dorsal fin to mouth . The mouth is protractile, and the lower jaw juts out . Sizes are fairly small, typically up to about 12--18 cm (5--7 in), but T. chatareus can reach 40 cm (16 in). </P> <P> Archerfish are popular for aquaria, but difficult to feed since they prefer live prey . </P> <P> Archerfish are remarkably accurate in their shooting; an adult fish almost always hits the target on the first shot . They can bring down insects and other prey up to 3 m (10 ft) above the water's surface . This is partially due to their good eyesight, but also to their ability to compensate for the refraction of light as it passes through the air - water interface when aiming at their prey . They typically spit at prey at a mean angle of about 74 ° from the horizontal but can still aim accurately when spitting at angles between 45 ° and 110 ° . </P> <P> When an archerfish selects its prey, it rotates its eye so that the image of the prey falls on a particular portion of the eye in the ventral temporal periphery of the retina, and its lips just break the surface, squirting a jet of water at its victim . The archerfish does this by forming a small groove in the roof of its mouth and its tongue into a narrow channel . It then fires by contracting its gill covers and forcing water through the channel, shooting a stream that, shaped by its mouth parts, travels faster at the rear than at the front . This speed differential causes the stream to become a blob directly before impact as the slower leading water is overtaken by the faster trailing water, and it is varied by the fish to account for differences in range . It also makes this one of the few animals that both make and use tools, as they both utilise the water and shape it to make it more useful to them . Archerfish have been known to send a stream up to 5 metres (16 ft) but can shoot insects only up to 1--2 metres (3 ft 3 in--6 ft 7 in) away due to their limited accuracy . They are persistent, however, and will make multiple shots if the first one fails . </P>

Why does an archerfish need to be still
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