Fisherman Robert Davies, who caught the sturgeon

The fish - the source of caviar - was caught in Swansea Bay by Robert Davies, from Llanelli and sold at auction for £650 in Plymouth on Thursday.

Mr Davies said he had got the necessary permission from the Queen but wildlife officers say he has broken the law.

As they continue to investigate the allegations, officers have impounded the catch.

It is not illegal to catch or keep a sturgeon, providing it is offered to the Queen first and officers said if it had been given away for free or kept by the fisherman, no offence would have been committed.

We're all ending up looking rather foolish, to be honest

David Pessell, Plymouth Trawler Agents

The sturgeon is rarely seen in UK waters and is classified as a "royal" fish - a status granted by King Edward II.

The law decreed that every sturgeon which was caught belonged to the Treasury and had to be offered to the monarch.

This means that the Queen has to be consulted before anything is done with one.

Mr Davies said he had informed Buckingham Palace about his lucky catch, and was duly given permission to keep it.

But Pc Jon Needham, a wildlife crime officer with Devon and Cornwall Police, said it was an offence to sell or offer for sale sturgeon, a protected species.

The sturgeon weighed almost 264lb

Anyone found guilty of selling one fish could face up to six months in prison or a fine of up to £5,000.

"There is a great long string of potential offences," the officer said.

"We need to carefully look at the circumstances."

Mr Davies' father and fellow fisherman, Kevin Davies, 44, said: "We have really been left in the lurch. I telephoned the police personally, and they left me a bit in the dark.

'Won the jackpot'

"It was a fantastic catch, and you won't see anything like it for many years. It's a shame it landed up this way."

Nick Henry of Moby Nicks fish sellers, in Plymouth, said: "It's come all the way from Wales from the fishing boat of a small family business.

"They must have thought that they won the jackpot. But they'll end up with nothing, I'll end up with nothing.

"But it is interesting."

David Pessell of the Plymouth Trawler Agents said: "We're all ending up looking rather foolish, to be honest.

"The Department of the Environment, the South Wales Sea Fisheries Committee, the Master of the Royal Household, Plymouth Trawler Agents, none of them knew that there was legislation preventing the sale of this endangered species."

Before the controversy blew up, Mr Davies, from Llanelli, who has been a fisherman for three years, said: "It was a normal day - apart from the fact I caught a valuable fish.

"To be honest, I didn't know what it was.

Trawler agent Dave Pessell said he had not known of the legislation

"I contacted fisheries and the coastguard and they came down and took some pictures and told me it was a sturgeon."

The sturgeon is usually found in the Caspian Sea, which is bordered by Russia, Azerbaijan, Iran, Kazakhstan and Turkmenistan.

Its eggs are used to make the delicacy caviar, which can cost several hundred pounds for a small pot.

The fish is rarely caught in the UK with as few as six believed to be landed each year.

A spokeswoman for Swansea Coastguard said that sturgeon, in common with other so-called royal fish like porpoise and dolphin, must be offered to the Queen if caught in the UK.

She added: "The fisherman caught it at around 1430 BST on Wednesday and got in touch with the Receiver of Wrecks, via the coastguard.

"A fax was sent to Buckingham Palace and fairly quickly a return fax came saying the fisherman was free to dispose of it as he wished.

"I believe that most of the time, fishermen are allowed to keep what they catch, although this has never happened in the eight years I've worked here."