The common carp (Cyprinus carpio)

[NorthernRaider]

Carp are THE species for this part of the world because the energy requirements are so LOW compared with the other species such as Tilapia or Trout / Char / Salmon.

Carp will only grow to the size of their environment, they exude a hormone into the water which determines how big they will grow.

Carps MAIN special consideration is two fold (1) Whilst they are happy living in turbid water heavy with plant material they don't like swimming in their own pee, (2) They MUST have a deep spot of at least 4ft 6 inches deep for them to over winter in.( below ground level, or 8 inches of high quality insulation around the pond if above ground.

You can enhance a Stew pond with the odd extra such as a TENCH and Swan mussels to eat the crap off the bottom of the pond, reeds around the edge act as filters, but a prefilter reed bed the the head of the pond is a better idea. You can use powered filtration so long as its an aerobic system.