The effect of temperature and salinity on the settlement and survival of copepodids of Lepeophtheirus salmonis (Kroyer, 1837) on Atlantic salmon, Salmo salar L.

The effects of temperature and salinity on the settlement, subsequent survi val and development of the copepodids of Lepeophtheirus salmonis on Atlanti c salmon were investigated experimentally. There was a significantly greate r settlement and survival of copepodids at 10 days post-infection (dpi) at 12 degreesC compared with at 7 degreesC at a constant salinity of 34 parts per thousand. Development of L, salmonis was also more rapid at 12 degreesC . Settlement was significantly greater at a salinity of 34 parts per thousa nd than at: 24 parts per thousand. In one experiment,survival at 10 dpi was significantly greater at 34 parts per thousand; however, a second experime nt found that there was no significant difference between the two saline le vels. This may have been because of a rise in water temperature for 2 dpi, which appears to have overridden the effect of low salinity. Development of L. salmonis was more rapid at 34 parts per thousand. Copepodids settled on all of the external surfaces of the salmon, although the proportion on dif ferent surfaces varied between experiments. The gills, particularly at low temperatures, the body surface, and the pectoral and dorsal fins were espec ially favoured.