Carp/Mud Marlin/Swamp Trout are a big pest species here in Australia and are taken out of the water and killed as soon as possible.
The local creek has a good supply of these mongrel things and my young fella and his mates have taken some big Carp out of the creek with the best by my son at 80cm and he reckons there's bigger 1's in there.
The other Carp were taken out of the same creek from a fishing comp our local pub fishing club had earlier in the year. The biggest was around 5kgs.