Chemical labeling of northern pike (Esox lucius) by the alarm pheromone of fathead minnows (Pimephales promelas).

In previous experiments, chemical stimuli from northern pike (Esox lucius) elicited fright responses from pike-naive fathead minnows (Pimephales promelas) only if the pike had recently eaten conspecific minnows. We used a behavioral assay to determine if the fright response is the result of the incorporation of the minnow alarm pheromone into the chemical signature of the pike. Because the alarm substance cells (epidermal club cells) of fathead minnows are seasonally lost by males, we used chemical stimuli from pike that had eaten breeding male minnows as a control stimulus. In independent laboratory and field experiments, pike-naive minnows exhibited fright reactions (e.g., increased shelter use, avoidance) when exposed to water from tanks containing pike that had eaten nonbreeding fatheads (with alarm substance cells), but not to water from tanks containing pike that had eaten breeding male fatheads (without alarm substance cells). These data indicate that the fathead minnow alarm pheromone chemically labels northern pike as dangerous to pike-naive receivers.