Its not suprizing that the carp population is so prolific in countries with a warm climate.
Carp were initially bred for food way back in the time of the Romans an were subsequently introduced into this country (UK) around the time that the Romans came over and settled.
The reason they were used for the table is several fold, ease of breeding, tolerance to unsatisfactory conditions, fast growth rates and large body mass.
As always once a species is introduced into an alien environment it will have some form of impact on the native species. In this case because the carp have been introduced into a warmer clime they are reproducing at an abnormal rate compared to their natural climate therefore creating problems to the native aquaculture and ecology.
Carp spawn in water temperatures exceeding 18oc and become prolific breeders at temperatures of 21oc+. When you think that a female can produce around 550,000 eggs per pound of body weight and the aelvin have a greater survival rate than most other species, its not suprizing that problems are then created.
As the battle then goes on for food within the waters, it then becomes a battle for survival which is again where the Carp's tolerance to poor conditions comes into play. As the native species find that the natural foodstock is depleting and the water quality due to higher levels of polutants due to excretions and insuficient oxygen rises, the inevitable happens and they become no more.
How would you get around this? The only option available is to effect a selective cull or removal. The second option in this case would be pointless because what would you do with the removed fish as no one wants them either.
It's just a shame that they can't be exported to third world countries for food rather than ploughed into the land as fetilizer but then again there is the cost to be weighed up.
Dave