Freshwater Stingrays Solve Problems With Tools : Discovery News

At least one species of stingray demonstrates the animal can be a clever problem-solver.

Fish have long been thought to be "simple reflex animals" but new research has shown that at least one species is capable of high-level cognition and even the use of tools.

The abilities of the fish in question, the freshwater stingray, even rival that of birds and mammals, researchers report.

Part of the reason these stingrays, which are common in the Amazon and related to ocean-going stingrays, has long been considered cognitively simple is that testing them is very difficult. Scientists at the Hebrew University of Jerusalem in Israel, however, were able to reach surprising conclusions with a battery of cleverly designed tasks.

When they placed food in a small plastic tube, the stingrays demonstrated a keen problem-solving ability by directing jets of water into the opening, forcing the food out. The jet of water, Dr. Michael Kuba, the scientist who led the research, explained, meets the basic definition of a tool. Following a study conducted by Dr. Benjamin Beck in 1980, researchers define tool use as "using an agent to achieve a goal."

Tool use is not unknown among fish. At least one other species, the archer fish, manipulates water in a similar way. Stingrays, however, had been lumped together with sharks, which have a similar skeleton made of cartilage instead of bone. Like sharks, it was thought, stingrays were "reflex machines having very acute senses but limited cognitive capacities."

The research, Dr. Kuba said, may lead to a better understanding of the "vertebrate thought process" and the evolution of vertebrate cognition.