Tough new rules were announced by Scotland’s Deputy Environment Minister Rhona Brankin at a meeting in Dundee on Monday.

Water bailiffs will now have the power to take offenders to court and fine them.

The move is part of the Executive’s crackdown on alien invaders which are destroying Scotland’s rivers and lochs.

Top of the hit-list is the American signal crayfish, which destroys river beds.

Another key target is the piranha-like English fish called the ruffe. It has infested Loch Lomond since it was introduced by fishermen in the early 1980s. Experts have warned it will wreck fish-farming operations and angling if it spreads.

An Executive source said: “Some people introduce these invaders into our rivers without thinking about the consequences.

“We hope these tough new penalties will make people think before they dump anything in our rivers and lochs.”

The new powers will be included in the Aquaculture and Fisheries Bill and should be on the statute book early next year.

The move on anglers is the latest step in a crackdown on alien invaders – both fish and plants – which are damaging the environment.

A hit squad has been set up to seek out and destroy non-native animals and plants.