Larval Settlement and Epidemiology of Lepeophtheirus salmonis KrOyer, 1837(Copepoda; Caligidae)

This study has been carried out to investigate the biological and environmental parameters influencing the settlement and post-settlement survival of the infective stages of Lepeophtheirus salmonis KrOyer 1837. The abiotic factors investigated were temperature and salinity. Temperature was found to have a significant effect on the settlement success of the copepodids with an inverse relationship between temperature and settlement. Survival of the louse at 10 days post infection showed a decrease at the reduced temperature. Temperature was also shown to have a direct relationship on lice development; higher seawater temperatures resulted in faster development. Regression analysis of temperature and settlement shows a significant correlation. A constant reduced salinity, 24%o, resulted in a reduced ability of the copepodid to infect its host compared with 34%o. Post-settlement survival in 24%o, at approximately 13°C resulted in 5.8% survival of lice to day 10 post-infection compared to 79% in 34%0 salinity. When this experiment was repeated but with elevated seawater temperatures of up to 18°C, survival at the reduced salinity was found to be 75.3%, higher than the ambient control group. The developmental rate at day 10 post-infection of L.salmonis larva at 24%0 was shown to be slower than development at 34%o. Distribution of the L.salmonis copepodid on its host showed the highest settlement on the gills and on the fins, particularly the pectoral and dorsal fins. Examination of L.salmonis survival at day 10 post-infection indicated the highest losses on the gills and the pelvic, caudal and dorsal fins. Settlement on the pectoral fins showed the highest settlement and the greatest survival.