| Summary: | Pink salmon (Oncorhynchus gorbuscha Walbaum) stocks in the Broughton Archipelago BC have seen a general decline in recent years. This is thought to be due to parasitism by sea lice, Lepeophtheirus salmonis (Krøyer, 1837), on pink salmon during early marine life stage. To investigate this, I measured swimming performance, an integrated measure of fish health, and post-swim body ion concentrations, a secondary stress response, of control and sea lice infected juvenile pink salmon (mass < 3.0 g). Using five different protocols (ranging in duration from 8 – 112 min), four constant acceleration tests (rates between 0.005 - 0.053 cm s₋²) and a repeated critical swim speed test, it was found that the final swimming speed of juvenile pink salmon (mass <5.0 g) at baseline was independent of the swim protocol (P > 0.05). Given this finding, estimates of swim performance in juvenile pink salmon can be accurately measured with an acceleration test lasting < 10 minutes. Using a repeated, constant acceleration (0.05 cm s₋²) protocol, the effects of sea lice on swimming performance and post-swim body ion concentrations were measured in artificially infected river-caught (RC-fish, mean body mass 0.3 + 0.05 g) and ocean-caught infected (OC-fish, mean body mass 1.1 + 0.1 g) juvenile pink salmon. Infection levels ranged in intensity (1 - 4 sea lice per fish) and development stage (chalimus 1 - adult). Swimming performance of RC-fish was not affected by lice intensity (P>0.05) but was affected by lice stage with swimming performance decreasing at chalimus 3 stage (-20.4%) and even further at more advanced sea lice stages (chalimus 4, -26.5%; motile, -37.9%). Sea lice parasitism had no significant effect on the swimming performance of larger OC-fish when compared to control. The absence of an additive effect on swimming performance of 1 to 3+ sea lice per fish suggests drag forces induced by the ectoparasite was not a major factor. In contrast, post-swim body Na⁺ and Cl- concentrations were typically elevated in infected compared to control RC-fish (P < 0.05), but not OC-fish (P > 0.05).
|
|---|