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Abstract

Groups of four Atlantic salmon parr were established and the dominant individual identified. Feeding responses were then observed in the remaining (subordinate) fish housed in one of three conditions: in the same compartment as the dominant fish (full exposure), separated from it by a transparent partition (visual exposure) or behind an opaque partition (isolated). Subordinate parr in the full exposure condition responded to and ate fewer food pellets than did the dominant fish. However, subordinate parr in the visual exposure condition and in the isolation condition fed actively, indicating that neither visual intimidation nor long-term stress-induced reduction of appetite were responsible for the reduced food intake of subordinate parr in direct contact with dominants. Dominant parr and subordinates in the visual exposure condition, but not subordinates in the exposed condition, moved further from their feeding station when attacking food items that were contested by a competitor compared with the distance moved for uncontested items. The presence of a competitor therefore forced both dominant and visually exposed subordinates to pay higher costs while foraging.