USA (6 Oct 2002) -- Archer fish are better than the best baseball players at predicting where plummeting prey will land, suggests a new study. They need only one glance. The fish (Toxotes jaculatrix) shoot water jets from their mouths at insects perched overhead. After a hit, they have to guess where their lunch will land, and get to it before it's gobbled by fellow fish. "It's very important for them to be quick," says Stefan Schuster of Albert Ludwigs University in Freiburg, Germany. He took high-speed videos of the fish and found it takes them just a tenth of a second to judge when and where in the water their food will fall. They then flip towards their target and swim there without looking back. Humans catching a ball thrown from far off, as in baseball or cricket, don't make just one prediction on where best to stand to secure the match-winning catch. We look repeatedly at the ball to alter our steps, which usually take a curved path. It is not clear whether the fish calculate each trajectory from scratch, or whether they take a best guess based on previous triumphs. "I expect experience plays a large role," says Schuster, who now plans to look into this. Hoverflies use similar predictions to intercept other flies when mating, says Thomas Collett of Sussex University, UK, who blew peas at them with a peashooter to study how they set a collision course. But hoverflies have a fairly standard size and speed. Archer fish shoot prey of a variety of sizes that fall at different speeds. This makes their decisions far more complex. "This mechanism varies a lot in different species," says Collett. SOURCE - Nature, CDNN | |  |
ARCHER FISH - Toxotes jaculatrix | Archer Fishes are famed for their ability to shoot down insects and small creatures resting on foliage or mangrove roots. In fact, Toxotes means "bowman" or "archer". Their flattened body presents a narrow profile from above, so they can sneak up on their prey. The bold black-and-white markings camouflage them in the sundappled water under mangrove vegetation. Main features: Can grow up to 40cm, but usually about 25cm, and weigh up to 750g. Flattened, knife shaped body. Genders look alike. Common in mangroves. World distribution: India, Southeast Asia, Australia, the Western Pacific. Classification: Family Toxotidae. Only one genus, world 6 species. How do they shoot? Archer Fishes are like submarine water pistols and can spit out a strong and accurate jet of water. With their tongue against the groove on the roof of their mouth, they form a tube, and force water powerfully out by snapping shut their gills. To get a good jet of water, the snout sticks out of the water, but the rest of the fish remains underwater. They direct the jet of water with the tip of their tongue. For accurate aim, they have large eyes located very near the mouth, which give good binocular vision. Their eyes, however, do not automatically correct for refraction, and they have to learn how to do this. The position of least distortion is directly below the prey, and the fish soon learn that this is the best shooting spot. The fish can squirt up to 7 times in quick succession, and the jet can reach 2-3m, but they are accurate to only about 1-1.5m. Fish as small as 2-3cm long can already spit, but their jets reach only 10-20cm. Once the jet of water knocks down the titbit, the fish gulps it down in its large deep upwardly directed mouth. If the blast doesn't knock down the prey, sometimes the weight of the water on the wings causes the insect to lose its grip and fall. Other ways to get their lunch: Archer Fishes, however, prefer to leap out of water to grab the prey in their jaws when it is close enough. When the leap fails, they may then resort to spitting. Archers usually swim in shooting parties. Often, several shoot at the same prey, and shoot relentlessly. When the prey finally falls, all rush to grab it. As the sharpshooter doesn't always get the prize, if the prey is within reach, the fish prefers to leap out of the water and grab it in its jaws. A prey in the mouth is worth two spat at! They can jump up to 30cm high. But Archer Fish don't just eat above-water prey. They also hunt small aquatic creatures and fishes, sometimes swimming in deeper water to catch these. Breeding: It is believed that only the juveniles are found in brackish water while the adults are more solitary and swim out to the coral reefs to breed. 20,000-150,000 eggs are laid. Only a few reach maturity in 1-2 years. Young fish have iridescent yellow patches on their upper body between the dark bands, which perhaps helps them to school together in the muddy waters. As they get older, patches disappear and the black bands get shorter and eventually only seen on the uppermost part of the body. Role in the habitat: Found in brackish water in mangroves and estuaries and sometimes further inland in fresh water. Status and threats: Archer fish control populations of their prey. They are also food for others higher up on the food chain. Although Archers are fairly common, they are threatened by the destruction of mangroves and by collection for the pet trade. Two Southeast Asian species are collected for the aquarium fish trade. They are not bred in captivity. (Natura) |
|
SCUBA FORUMDISCUSS THIS TOPIC - Dive in and have your say at Scuba Forum |
