An investigation into the larval energetics and settlement of the sea louse, Lepeophtheirus salmonis, an ectoparasitic copepod of Atlantic salmon, Salmo salar

This study was undertaken to investigate the energy levels of Lepeophtheiru s salmonis larvae and test the hypothesis that aged lecithotrophic copepodi ds would have reduced settlement ability. Calculated energy levels for all pre-settlement stages were determined following Carbon: Hydrogen: Nitrogen analysis. The calculated energy levels of winter parasitic copepodid larvae (approx, 7800 cal/g dry weight) were similar to those of winter free-livin g copepod larval stages. Energy levels of copepodids were found to decline sharply between those aged day 1 and 2 post moult and between those aged da y 5 and 7. Settlement experiments with aged copepodids, at summer and winte r sea water temperatures showed a statistically significant difference in s ettlement ability between copepodids aged 7 days and those aged 1 and 3 day s. However, once attached and settled on the host the rate of development a nd initial survival was found not to be statistically different from that o f the other age groups that were examined. Copepodid durability, as a free swimming stage, and its ability to infect the host in appreciable numbers o ne week after moulting to the infective stage will have important implicati ons for the salmon culture industry.