Sea lice infection of juvenile pink salmon (Oncorhynchus gorbuscha): effects on swimming performance and postexercise ion balance

Sea lice (Lepeophtheirus salmonis) infection negatively affected swimming performance and postswim body ion concentrations of juvenile pink salmon (Oncorhynchus gorbuscha) at a 0.34 g average body mass but not at 1.1 g. Maximum swimming velocity (Umax) was measured on over 350 individual pink salmon (0.2–3.0 g), two-thirds of which had a sea lice infection varying in intensity (one to three sea lice per fish) and life stage (chalimus 1 to preadult). For fish averaging 0.34 g (caught in a nearby river free of sea lice and transferred to seawater before being experimentally infected), the significant reduction in Umax was dependent on sea lice life stage, not intensity, and Umax decreased only after the chalimus 2 life stage. Experimental infections also significantly elevated postswim whole body concentrations of sodium (by 23%–28%) and chloride (by 22%–32%), but independent of sea lice developmental stage or infection intensity. For fish averaging 1.1 g (captured in seawater with existing sea lice), the p...