I've just built a pond in my back yard (its about 5ft by 5ft and 4ft deep). i would like to stock with some exotic fish and maybe koi carp. could you please give me some ideas on which fish i could put in it.?

It sounds like you've got about 1000 gallons there (LxWxDx7.48 gal/cu.ft.), but you have not told me what kind of filtration or water circulation you have installed.

If all you have at present is a hole in the ground with water in it, I strongly suggest that you immediately fill it back up with dirt before mosquito season.

If you have a small submersible pump feeding a fountain or waterfall, you can put plants and a few goldfish into it, but not koi. Koi require intensive filtration, and if you are planning on this you will need a filter and pump capable of serving and bioconverting at flow rates of 1500 gallons per hour. You will need filter media that is at the high end of the "surface area per cubic foot of space occupied" formula to give your biological filtration bacteria someplace to stand and work.

Plan on at least 50 gallons of water for every inch of koi if the fish are smaller than 8 inches long. For larger fish, double this, and always remember that koi grow rapidly. Do not try to mix koi with native species such as bass or perch. The native fish are predators, and will bully and/or eat your decorative fish.

(Answer courtesy Bob Passovoy)