The species of bream is normally found in the balmier waters of the Mediterranean and South Africa, was found by fisherman Andy Giles in his nets in the English Channel.
Mr Giles, 38, caught the fish, which is instantly recognised by its gold stripes running along its body, six miles south of Polperro, Cornwall.
"We were trawling for lemon sole and hauled up the net at the end of the day and almost immediately saw this striped fish, we didn't have a clue what it was," he said.
"I had never seen one before and after taking a photograph of it I tried to look it up on the internet and called some friends to see if they knew what it was.
"I put it in the fish box and brought it back for experts to have a look at it.
"Now I realise what it was and the effects it can have, perhaps I should have taken it into town to sell to some clubbers!"
There have only been three previous recordings of sarpa salpa in British waters before, with one of them being off the Channel Islands in 1983.
James Wright, a senior biologist at the National Marine Aquarium in Plymouth, said: "These are a fairly common fish off Tenerife, Malta and Cyprus but it is very rare to get them this far north.
"It could be a single fish that was shoaling with a different species but it could be that there are more of them in our waters."
Sarpa salpa are a popular dish in many Mediterranean restaurants.
But according to marine experts, certain species of plankton-eating fish, like the sarpa salpa, can give off hallucinogenic fish poisoning if the heads or other body parts are consumed.
The effects include vivid hallucinations within minutes of eating it which can last for days.
In 2006 two men, one aged 90, were hospitalised in the south of France after eating sarpa salpa.
The elderly man suffered from auditory hallucinations a couple of hours after eating the fish followed by a series of nightmares over the next two nights.
The younger man, aged 40, endured similar effects which took 36 hours to disappear.
) so I don't think I'd want to try that!
