Two men have admitted a string of offences in what will be seen as a test case in the fight to stop fish being taken for food from Britain's rivers.
Gunars Kaspers and Oleg Stepin were arrested after police swooped on Norfolk's River Wissey.
The alarm was raised after a group of men were seen using boats to set nets across a remote stretch of the Fenland river in May.
Detectives and Environment Agency fishery officers found them barbecuing pike and bream on the bank at Roxham Fen, between Hilgay and Wissington.
Live tench and perch were found on a crude stringer made from a clothes line and gill nets and a pair of boats were confiscated.
Kaspers, 39, and Stepin, 43, have entered guilty pleas to stealing fish, fishing during the close season, fishing with an unlicensed instrument and the use of an unregistered vessel.
Both are due to be sentenced by magistrates next week. Another man arrested at the scene has failed to answer bail, while a 35-year-old man has been told no further action will be taken.
The arrests came after high-profile campaigns to highlight the problem of fish theft by King's Lynn Angling Association and the Pike Anglers Club.
A Crimestoppers-style hotline was set up after both groups met with EA officials to discuss their concerns.
Lynn AA changed its bylaws to outlaw the taking of fish from its waters, which include stretches of the Wissey, Great Ouse and Little Ouse, along with drains and stillwaters.
The PAC set up a kitemark scheme for bait dealers, following claims fish were being stolen wholesale for the bait trade.