Behavioural interactions of sea lice, threespine sticklebacks, and juvenile Pacific salmon

There is scientific controversy over the role played by sticklebacks (Gasterosteus aculeatus) in transmitting sea lice (Lepeophtheirus salmonis) to juvenile pink salmon (Oncorhynchus gorbuscha). Sticklebacks could be either ‘sources’ or ‘sinks’ for sea lice infecting salmon. I investigated host choice of adult male lice and a novel cleaning behaviour by sticklebacks towards juvenile salmon. Behavioural assays showed that sea lice preferred water that had contained salmon over controls, with no preference between salmon and stickleback cues. Infection trials showed that lice had lower survival on sticklebacks than on salmon. Experiments showed that cleaning behaviour by sticklebacks reduced louse loads on salmon. Sticklebacks preyed more strongly on adult female lice than males, and they also cropped their egg-strings. These results suggest that sticklebacks are unsuitable hosts for sea lice and cleaning could potentially reduce sea louse populations. Thus, sticklebacks are more likely to be ‘sinks’ for sea lice than ‘sources’.