PRODUCTION OF NAUPLII OF LEPEOPHTHEIRUS-SALMONIS (KROYER) (COPEPODA, CALIGIDAE) FROM FARMED AND WILD SALMON AND ITS RELATION TO THE INFESTATION OF WILD SEA-TROUT (SALMO-TRUTTA L) OFF THE WEST-COAST OF IRELAND IN 1991

The number and fecundity of ovigerous Lepeophtheirus salmonis (Kroyer) infesting wild and farmed salmon and daily production, from these fish, of nauplius I of L. salmonis was estimated for a number of areas off the west coast of Ireland between March and July 199 1. Significant differences in body size and fecundity of the parasite were apparent both over time and among sampling sites. Body size and egg number were positively correlated. Lice infesting wild salmon were larger and carried approximately twice as many eggs as those infesting farmed salmon. Farmed salmon contributed 95% of the total production of nauplius I of L. salmonis in the mid west co ast region. Production ranged from 0 to 3.8 x 10(7) nauplii per day from salmon farms in individual embayments. Using data from six embayments the production of nauplius I during mid April was correlated with parasitic intensity of L. salmonis infesting wild sea trout (Salmo trutta L.) 3 weeks later. Although the production of nauplii remained relatively constant between March and July, transmission to sea trout was apparently restricted in time to late April and May. Temporally varying susceptibility to infestation may therefore have a role in determining the level of infestation that develops.