Two boys caught a one-metre/40" sturgeon off the Welsh coast at the weekend - using a sausage as bait.
The youngsters were fishing off Hobbs Point, near Pembroke Dock when they made the rare catch.
The last time one of these fish was caught in UK waters was back in 2004.
Now fishermen along the coasts of England and Wales are being asked to watch out for more of the sturgeon, which is a protected species.
It is illegal to retain sturgeon and anybody catching one should return it quickly unharmed and alive to the water and then report it to either their local Inshore Fisheries and Conservation Authority (IFCA) or to Cefas.
Steve Colclough, of the Institute of Fisheries Management (IFM) said: "Before putting it back they should note as many facts as possible - its length, overall condition, signs of damage or disease, the data on any tag attached to it and take a good photo.
"A yellow tag would show the fish had probably migrated from the Gironde, in France, where the European sturgeon is now being bred and released.
"These fish would normally stay in the Gironde until they were about ten years old and they might then migrate to the open sea.
"If they came to the UK they would most likely be caught in estuaries and still be juvenile fish. Normally they would live 50 or 60 years and grow up to three metres long."
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