FAMILIARITY AND SHOAL COHESION IN FATHEAD MINNOWS (PIMEPHALES-PROMELAS) - IMPLICATIONS FOR ANTIPREDATOR BEHAVIOR

We exposed groups of four fathead minnows (Pimephales promelas) that w ere familiar to each other and had been taken from naturally occurring shoals, and groups of four fish unfamiliar to each other, taken from four separate shoals, to either chemical stimuli from pike or a model fish predator (northern pike, Esox lucius). In response to both chemic al stimuli from pike and the pike model, minnows from familiar groups showed greater shoal cohesion than those from unfamiliar groups. Tight er shoal cohesion should result in a higher probability of surviving a n encounter with a predator. Fish in familiar shoals also exhibited mo re dashing, a known antipredator response, than those in unfamiliar gr oups. In addition, groups of familiar fish showed less freezing behavi our than unfamiliar groups. In response to the model fish predator, fa miliar shoals exhibited a greater number of predator inspections, and the number of inspectors per inspection visit was greater, than those in unfamiliar groups. These results suggest that preferential shoaling with familiar conspecifics leads to an increase in cooperative antipr edator behaviour and may thereby lower a minnow's risk of predation.