Fish blend quickly into the background.

People may start calling quick-change artists flounders rather than chameleons, thanks to a new study on the camouflage habits of Bothus ocellatus.

In less than 8 seconds, these tropical flounders can transform their markings to match even unusual patterns put on the floor of their laboratory tanks, report Vilayanur Ramachandran and his colleagues at the University of California, San Diego. When swim ming over sand, the flounder looks like sand.

But if the tank has polka dots-no problem, the fish develops a coat of dots.

In the ocean, flounders change their appearance to avoid predators or to sneak up on prey. Although these fish have a reputation for altering their markings or color to blend in with their surroundings, few studies have systematically analyzed such dramat ic changes, says Ramachandran.

He and his coworkers laid gravel, a checkerboard, a gray sheet, or yellow beach sand at the bottom of tanks. They then put five flounders, one at a time, in each tank. Each fish quickly changed its skin to resemble the floor patterns, the San Diego scient ists report in the Feb. 29 Nature. The fish changed their markings even faster-in as little as 2 seconds-when exposed to a pattern for the second or third time.

B. ocellatus features at least six types of skin markings, including H-shaped blotches, small dark rings, and small spots, the researchers report. The fish adjust the darkness of these figures to blend into the different backgrounds.

The scientists have yet to examine the neural mechanisms that enable a flounder to alter its spots. However, cells in its visual system may respond specifically to shapes in its environment. These visual cells may then signal pigment cells in the skin to produce large or small splotches, Ramachandran speculates.

The flounders' colors, as well as patterns, change in response to the background, the researchers note.

The San Diego group's report refutes a 1988 claim by William M. Saidel of Rutgers University in Camden, N.J., that flounders have little capacity for adaptive pattern changes. However, Russell D. Fernald, a neuroscientist at Stanford University, points ou t that Saidel studied flounders from the deep, cool waters of New England, where fish may require fewer camouflage outfits.

"I think [the new study] is a modest advancement" in what we know about how flounders change their markings, says Saidel. For example, the study finds that the time the fish take to transform their appearance is at least 30 seconds shorter than previous r eports, he says.

Ramachandran is something of a quick-change artist himself. As a neurologist, he normally studies humans. However, he finds the flounder so intriguing that he sometimes takes on the role of ichthyologist.