Alarm cue specificity and response ontogeny in juvenile rainbow trout (Oncorhynchus mykiss)

Many aquatic prey animals release chemical cues upon being captured by a predator. These chemical cues, referred to as alarm cues, may act to warn nearby individuals of danger. For the cues to be useful, fish must be able to discern if they are indicative of a real threat; cues from conspecifics in different age groups may be irrelevant due to size-and habitat-related shifts in predation risk. We test the response of newly-hatched rainbow trout, Oncorhynchus mykiss, to three concentrations of alarm cues from conspecifics from two age groups: newly-hatched versus six-month-old juveniles. Newly-hatched trout demonstrated a significant fright response to all three concentrations of alarm cues, but showed no difference in strength of response based on either concentration or age of the cue donor. We propose that the newly-hatched trout did not respond differently because of the high risk of predation that they face during this life stage.