The Scottish Government has launched an investigation after a bullet shell was found during an inspection of a fish farm off North Uist.
The use of drugs at fish farms in Scotland has risen more than 50 times over the last six years.
Ten lochs across Scotland have been polluted by a toxic pesticide used by fish farms to control fungus, parasites and disease.
A £3 billion fish farming multinational in Scotland has been officially reprimanded for animal welfare failures after more than 700,000 caged salmon died over three months.
The Scottish Government defied concerted pleas by salmon farming multinationals to keep photos of diseased and damaged fish secret, according to internal emails.