Aquaculture problems: Parasites and disease
More fish farms mean more hosts for parasites - indeed, in some parts of Northern Europe, sea lice numbers are now significantly higher as a result of the millions of farmed fish in the sea. Just 10-15 sea lice can kill a fish.
Wild fish can also be exposed to viruses and other diseases through the use of imported, unprocessed fish to feed farmed fish. This problem is particularly associated with farmed tuna, which are usually fed whole fish rather than processed fish pellets.