Abstract:
Fish farmed in sea cages may become infested by parasites from wild fish, and in turn become point sources for parasites. Sea lice are the best studied example of this risk. They are the most significant parasite in salmon farming in Europe and the Americas, costing the aquaculture industry US$400 million a year. A recent review indicates that they are also pathogenic to some wild fish under natural conditions. Epizootics are rare in wild fish populations, but have occurred on wild fish in areas where farms have sea lice infestations, notably Europe, east and west coasts of North America, and Chile. Recent r e v i e w s a n d m o d e l l i n g s t u d i e s n o w p r o v i d e a n u n d e r s t a n d i n g o f t h e mechanisms of how the salmon louse, Lepeophtheirus salmonis, can infest wild salmonids from farm sources. Three-dimensional hydrographic models predict the distribution of the planktonic salmon lice larvae best when they include wind driven surface currents and larval behaviour. Caligus species can also cause problems on farms and transfer from farms to wild fish, and this genus occurs worldwide. The increasing evidence that lice from farms are a significant cause of mortality on nearby wild fish populations provides a c h a l l e n g e f o r t h e f a r m s t o c o n t r o l l i c e , b u t a l s o r a i s e s c o n s e r v a t i o n , e c o n omi c , a n d p o l i t i c a l i s s u e s a b o u t h ow t o b a l a n c e a q u a c u l t u r e a n d fisheries resource management. Current and possible additional strategies to control lice are outlined.
