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

Abstract

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 presence of sea lice had no significant effect on either Umax or postswim whole body ions. Thus, a single L. salmonis impacted swimming performance and postswim whole body ions of only the smallest pink salmon and with a sea louse stage of chalimus 3 or greater.

Physiological consequences of the salmon louse (Lepeophtheirus salmonis) on juvenile pink salmon (Oncorhynchus gorbuscha): implications for wild salmon ecology and management, and for salmon aquaculture

“…When two to three copepodids attach, a significant effect occurs after 15 days when the chalimus 3 stage is reached [12]. For the same cohort of pink salmon, infection with a single copepodid reduced U max after 15 days when the chalimus 3 stage is reached [13]. However, none of these sublethal effects is evident once pink salmon reach about 0.5 g, which would typically take about one to two months of normal growth.…”

“…A repeat-maximal swimming performance (U max ) protocol that had been specifically developed for juvenile pink salmon [57] was used to assess the effect of different salmon louse loads and developmental stages on swimming performance. U max was significantly reduced by a single sea louse once it reached chalimus 3 stage (where both louse and salmon developed together) provided the pink salmon was less than 0.34 g. Impaired U max in infected fish was associated with elevated whole body ion levels, indicating an ionoregulatory disturbance [13]. However, the impairment of U max was not related to louse load as predicted, because there was no statistically significant difference in U max among salmon louse loads of 1, 2, 3 or more lice/fish.…”

“…In contrast, unhealthy fish and poorly prepared smolts have ionoregulatory disturbances at fatigue and repeat swimming performance is reduced by up to 33 per cent [55,56]. Therefore, exercise capacity is used as a tool to assess physical condition that is thought to have ecological relevance [59] and therefore may be a useful indicator of ecological fitness [13]. It is not surprising that at some point salmon louse will impair swimming performance; however, whether this impairment is seen at ecologically relevant levels of infection is of primary interest.…”

“…Given that 10 per cent of wild juvenile pink salmon were infected with salmon lice at an intensity of about one for the past several years [61], the management implication of this work is that up to 10 per cent of the juvenile pink salmon in the Broughton Archipelago may exhibit sublethal effects of salmon louse exposure. However, what this ultimately means in terms of fish survival remains unknown [13]. …”

“…Therefore, a large group of artificially infected pink salmon were able to shed 75-80% of the initial number of attached lice after 14 days, while some individuals shed four or more salmon lice. Thus, reporting the physiological effects of salmon louse infection relative to the infection intensity at the time of sampling, which we do [12,13], is conservative in that many of those fish may have been infected with a higher intensity at some point.…”