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Smart fish that spit

Banded archerfish, Toxotes jaculatrix. Image credit: James St John

AUSTRALIA IS A hotspot for spitting fish, boasting four of the world’s seven species of archerfish. In nearly every river in northern Australia archerfish can be detected lurking near the surface, although seeing one shoot a jet of water at an insect requires luck.

These fish are becoming popular around the world in tests of animal intelligence. In one experiment at the University of Queensland an archerfish showed it could recognise  44 different human faces. The computer-generated faces were all similar, with the same flesh colour and no hair, forcing the fish to rely on features such as height of the forehead or architecture of the nose to decide if two faces shown together were the same. Archerfish are ideal for such tests, not only because they can see well out of water, but because they can declare choices by spitting at a screen to earn a food reward.

Toxotes jaculatrix. (Image Credit: James St John)

These fish are impressive operators in other ways too. They can hit an insect flying rapidly away by aiming judiciously ahead of it. Most of the time they spit at ants or other crawling insects on overhanging foliage, hitting them from up to two metres away to dislodge them. Archerfish are not hampered by the water surface distorting their view of the world above and, although they protrude their snouts before spitting, keep their eyes in the water.

Archerfish travel in small groups in which no rules of fairness seem to apply. The fish that dislodges an insect often isn’t the fish that eats it. Up to 60 per cent of food items hitting the water are grabbed by a bystander rather than the shooter.

Whenever you visit a riverbank in northern Australia you have a good chance of seeing these fish. The sevenspot archerfish (Toxotes chatareus) and banded archerfish (T. jaculatrix) are common in Australia and stars of experiments and YouTube clips. Both can live in salt and freshwater, and have ranges extending from tropical Asia to Australia and Melanesia. Lorentz’s archerfish (T. lorentzi) is found only in Australian and New Guinean rivers, and the Kimberley archerfish (T. kimberleyensis), which only gained its scientific name in 2004, keeps to a few rivers in the Kimberley.

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