Response of Fathead Minnows (Pimephales promelas) to a Chemical Alarm Signal

Abstract

The fathead minnow, Pimephales promelas, and common shiner, Luxilus cornutus, are cyprinid fishes native to Minnesota. Both species produce a chemical alarm signal, hypoxanthine-3-N-oxide (H3NO), in response to injury to the skin. H3NO may therefore indicate that a predatory fish is nearby. The objective of this study was to examine the behavior of fathead minnows in the presence and absence of chemical alarm signal isolated from conspecifics. Behaviors were studied under several conditions: solitary fatheads, single species schools of 12 fatheads, or mixed species schools of nine fatheads and three common shiners. Two synchronized digital camcorders were used to monitor the vertical and horizontal movement of individuals or schools, proximity of individuals, and size of shoals. In the absence of alarm chemical signal fatheads and common shiners exhibited different behaviors. Both solitary fatheads and shoals exhibited greater vertical movement than common shiners, which aggregated near the bottom of the tank. Solitary fatheads displayed reduced movement both vertically and horizontally in response to H3NO. Although vertical movement of fathead shoals was reduced after the addition of chemical alarm signal, horizontal motion continued in most trials. Fatheads in shoals adopted a testing or sampling behavior. Individuals made looping motions, moving a few centimeters vertically and quickly returning to the bottom of the tank. In summary, the behavioral response of fathead minnows was different when solitary or in shoals.