Visual and olfactory stimuli in learned release of alarm reactions by zebra danio fish (Brachydanio rerio)

Alarm reactions, innately organized antipredator defensive behavior, are precipitated in zebra danio fish (Brachydanio rerio) by a pheromone, alarm substance, passively exuded from injured skin of conspecific fish. Control over inducement of alarm reactions from fish can be transferred to other stimuli that do not initially provoke alarm. This was first found when an olfactory stimulus (morpholine) presented to fish together with alarm substance elicited alarm behavior from the fish and transformed morpholine into a learned elicitor of alarm from the fish. We observed similar behavior here where fish learned to react to an initially neutral visual stimulus (red light). We also confirmed earlier findings of social transmission of predator recognition by zebra danios. Fish trained to alarm react to light and morpholine were mixed with completely naive fish and tested with light and morpholine alone. All fish in the combined group displayed alarm. The naive fish, separated out and retested with light and morpholine, also exhibited alarm. Thus, the naive fish, never exposed to alarm pheromone, nevertheless learned to recognize predator cues that were socially transmitted by conspecific behavior.