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Fish TV and a new way to swim

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How do tiny sea creatures, many only one-tenth the size of a grain of rice, stay together to form the dense patches that whales and other creatures rely on for food? Why don't these crowded groupings of animals break up by sinking deep or floating to the surface?

The answer to these questions sounds like a description of the best water park ever: in order to maintain their preferred depth, the animals swim against jets of water that shoot up from the sea floor and pound down from above.

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Using a tool called "Fish TV," the scientist caught the sea creatures swimming against the flow of vertical jets of water.

The scientists are so excited about the finding that little sea creatures swim against the vertical flow of water to maintain a constant depth in the water because they've been looking for behavior for more than 50 years.

Click here for a high resolution photograph.

The scientists observed the zooplankton in a column of water that is moving down toward the sea floor and saw that the creatures were swimming up toward the surface. Also, the creatures swam down when they drifted into a column of water moving up toward the surface.

To catch the animals in action, Amatzia Genin from the Hebrew University in Eilat, Israel and his colleagues watched this swimming technique on their Fish TV. This device shoots out sonar that hits the hard shells that protect some zooplankton. An echo bounces back. Using this echo, as well as precise observations about ocean currents, the scientists studied the movements of the animals.

The scientists set up the FishTV at the bottom of the Red Sea off the coast of Eilat, Israel and off the coast of Sinai, Egypt. They clocked the microscopic animals swimming at speeds of up to 10 body-lengths per second.

In the future, the scientists hope to explain how the zooplankton know how deep in the water they actually are.

Their research appears in the 06 May, 2005 issue of the journal Science.