A crackdown is under way to combat large-scale poaching from lakes in the north east of the country.
Paddy Greene, an inspector with the Eastern Regional Fisheries Board, said three seizures of fish and equipment had been made over the past 10 days.
It is believed that some of the people involved in the poaching in the lakes between north Meath and north Monaghan are originally from Eastern Europe.
"They have been using a number of illegal methods including the use of Otter Boats . . . these are illegal instruments that they plant out on the water and are very efficient at killing fish. They are also . . . using nets, and they would also be killing large numbers of coarse fish by rod and line. But in this instance it is the other illegal dealings that we are concerned with," he said.
The seizures were made at Drumeske Lake near Monaghan town, Milltown Lake near Castleblayney and at another lake near Carrickmacross.
"There is an ongoing general problem with the killing of coarse fish even by legal means," he said. "Anglers and UK visitors all return the fish alive to the waters, but foreign nationals tend to kill those fish as it is part of their culture."
New bylaws have recently been introduced that aim to prevent anglers from killing large numbers of fish by rod and line through limits of four fish per day.
"We have gangs and people operating totally illegally with nets and traps," the inspector said. "If we don't get to grips with it, it will affect tourism."
Signs and leaflets have been drawn-up in various languages to ensure people understand the bylaws in operation to protect fishing stocks.
Mr Greene warned anyone caught illegally poaching could expect stiff fines and the seizure of their gear and any fish caught.