Grass Carp – a successful alien invasion?

This thread has been prompted by some of the questions raised during discussions on the ‘Returning non-native species’ thread.

Many stockings of Grass Carp were carried out over 10 yrs ago with the permission of EA and properly licensed under the (then) current regulations. The fish were allowed as part of weed control programmes and part of the attempts to reduce algal blooms which were seen as a danger to environmental health at the time.

The original theory was that because Grass Carp had an abbreviated digestive system they needed to eat large quantities of vegetable matter (3 times their body weight daily) to survive – producing ‘grass pellets’ which could feed other coarse species. They thus seemed like the ‘answer to a maidens prayer’ in that they cleared weedy lakes and produced food for other fish – with no side effects other than being a fast-growing fish for anglers! With a 10-year life and triploidy they wouldn’t have any long-term ill-effects in terms of being an invasive non-native species! A win-win allround!

What’s the overall concensus on Grass Carp – a successful experiment in weed control – or a waste of time and effort becoming just another zoo fish?
Have they produced any detrimental side-effects on fish / fisheries?

Comments please?

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