Alarm reaction of Iowa and johnny darters (Etheostoma, Percidae, Pisces) to chemicals from injured conspecifics

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Abstract
Two species of darter show reduced activity when they detect chemical stimuli from an injured conspecific. This is an appropriate response to a predator warning signal in bottom dwelling fish such as darters. Predation on darters by northern pike releases sufficient chemical stimuli to elicit the reduced activity response. Skin extract is more active than muscle extract in releasing the response. Darter skin contains large, nonmucous secretory cells that may contain the alarm substance. This alarm system in percid fishes appears to be analogous to the better known alarm substance (Schreckstoff) system in ostariophysian fishes.