Effects of infochemicals on microhabitat choice by the freshwater amphipod Gammarus roeseli

Predator avoidance via alternative microhabitat choice by the freshwater amphipod Gammarus roeseli was examined in laboratory y-maze experiments, where predator presence was simulated by fish-conditioned water. The amphipod responses to three benthivorous fish species, which differ in their mode of feeding, were examined. G. roeseli avoided habitats with water conditioned by juvenile burbots (Lota Iota) and crucian carp (Carassius carassius), but not by juvenile Eurasian perch (Perca fluviatilis). Responses to predator-conditioned water only took place at high fish densities. Thus the amphipods were capable of distinguishing between acute predation risk, represented by high infochemical concentrations, and the low background level of infochemicals. The results of the study imply that proper microhabitat choice is an alternative to decreased locomotory activity, for enhanced survival of amphipods in the presence of fish predators in both lentic and lotic environments. A preliminary characterisation of the infochemical suggested that it is different from that which causes responses in Daphnia, as it could not be extracted by lipophilic solid phase extraction.