What Will the Lake Perch Do Next?

A Study Where River Water Meets the Lake

Where a river enters Silverfin Lake, researchers care for a young perch in a roomy floating research pen. Water flows through the pen, and plants provide shelter. The perch is used to eating small food pellets. Researcher Imani wonders how information about the pellets might affect where the fish swims.

Fish can receive sight information through their eyes. They can also receive smell information from substances in the water through sense organs inside their nostrils. Sense organs send information to the brain. The brain processes information and can use past experiences when guiding a response. A fish moves its fins and tail to change where it swims.

Imani prepares four food containers with the same size and shape. Each holds the same amount of pellets. A clear, sealed container lets the perch see the pellets but keeps their odor inside. An opaque container with mesh-covered openings hides the pellets but lets their odor enter the water. A clear container with openings provides both kinds of information. An opaque, sealed container hides the pellets and keeps their odor inside. The perch cannot eat pellets through any container.

An adult places one container at a marked spot without tapping or shaking it. A trial begins when the perch is at the same starting spot. Imani records whether it swims to within one body length of the container within 30 seconds. She changes the container type while keeping the fish, starting distance, pellet amount, and observation time the same. She also keeps lighting and water flow similar.

Each type has 12 short trials spread over several weeks. Trials take place at the same time before a regular feeding, and the order of container types is mixed. The perch receives its normal care and meals. Researchers record its movements, but they do not measure activity inside its brain. Their graph shows how often it approached each container.