Animal rights extremists have been blamed for freeing thousands of halibut from cages at a fish farm in Argyll.
Fish farm owners have been told to tighten security after the raid
Strathclyde Police launched an inquiry after 15,000 fish were released from the Kames Marine Fish Farm, near Oban.
It has been reported that the letters ALF - for Animal Liberation Front - were spray-painted nearby. The damage has cost the owner more than £500,000.
Police warned other fish farms to raise security after the raid between Wednesday night and Thursday morning.
The farmed halibut were released directly into the sea.
A spokesman at the Kames farm described the incident as "totally horrific and malicious".
"It has served no purpose to protect the fish at all because we are now finding hundreds of dead fish along the beaches," he said.
"It also has substantial financial implications to the business and our customers are extremely upset."
Detective Chief Inspector Neil Thomson said: "We are very keen to speak to local residents and motorists travelling on the A816 Oban to Lochgilphead road and also Degnish Road.
"They may have witnessed any suspicious activity in the Kilmelford area on Wednesday night or in the early hours of Thursday morning.
He said police were particularly keen to speak to the occupants of a two-toned Leyland Daf motor vehicle which was seen about 1900 BST in the Degnish Road area on Wednesday evening.
"These people could unwittingly have information that could be helpful to the investigation," he added.