Behavioural responses of naive Arctic charr young to chemical cues from salmonid and non-salmonid fish

The ability to distinguish among chemical cues from multiple predators is o f key adaptive value for many prey fish. We examined the attractiveness and repulsiveness of chemical stimuli from different coexisting fish species f ed on different diets on the behaviour of hatchery reared Arctic charr youn g in a Y-maze fluviarum, where the charr could choose between two sides eit her with control water or stimulus water with fish odour. We used stimuli f rom (1) matching sized conspecifics, large (2) Arctic charr, (3) salmon, (4 ) brown trout and (5) brown trout fed on Arctic charr fry. Other salmonids were given pellet food. Additional fish odour treatments included piscivoro us (6) pike and (7) burbot. In the control trials both sides received contr ol water. Arctic charr young were expected to respond adaptively to the sti muli from coexisting piscivorous fish. The charr most strongly preferred wa ter with the odour of their matching sized conspecifics, which was the only fish odour they were familiar with before the experiments. They also showe d significant preference for other salmonid odours, even though these fish are potential predators on small charr. Chemical stimuli from pike and burb ot, on the contrary, were strongly avoided, and burbot odour even prevented the charr to swim and enter the lateral halves of the fluviarum. Moreover, odour from brown trout fed on Arctic charr fry was avoided when compared t o stimuli from trout fed on pellets. Although the Arctic charr young were c ompletely naive regarding piscivores, the fact that;hey could distinguish b etween different predator taxa and diets on the basis of chemical cues only reflects the long coevolutionary history of these fish populations.