The Pike Anglers Club is calling for pike match organisers to stop using barrels to retain fish after claims pike died in poorly-stewarded competitions after being kept for long periods without oxygenation.
The latest scandal centres on events held on loughs in Ireland.
It comes after the 2,500-strong PAC called on the organisers of Ireland's most prestigious pike fishing competition to abandon the use of barrels over "serious welfare concerns", amid growing calls to boycott the event.
One PAC member who witnessed an event last weekend said pike which had been retained in barrels during a match were transferred to a holding tank.
He claims fish deaths were witnessed by a named fisheries officer, who the club is now trying to contact.
PAC secretary Mark Barrett said: "We are still trying to get to the bottom of what happened but if the accounts of an eyewitness are correct a substantial number of fish died.
"Barrels appear to be growing in popularity as a method of retaining pike prior to weighing in competitions held in Ireland.
"If reports are true - and we have no doubt the basic facts are - they clearly illustrate barrels are not a suitable means of retaining pike and anglers should avoid their use and events where this is encouraged."
The PAC has an eyewitness willing to go public. The club is also now in a position to release pictures of barrels used at last year's Erne International Pike Fishing Classic, which clearly show the containers are not aerated and fish would be retained in shallow water, on board a boat.
Talks between the PAC and organisers of the Fermanagh-based competition broke down in April.
The PAC said it had serious welfare concerns both over the use of the barrels and the lack of stewarding at the event, meaning pike would be retained for long periods or transported some distance to be weighed.
The club fears fish will be deprived of oxygen and pike stocks already under pressure could be further depleted. But organisers refused to budge.
The Erne International Pike Fishing Classic is being backed by a group of organisations dedicated to promoting tourism in Northern Ireland, including Fermanagh District Council and the Department for Culture, Arts and Leisure.
Hundreds of anglers from across Europe are expected to take part, from October 19 – 21.