Projectiles from a gun do not penetrate water with much force (especially shot guns) although I know several guys that would love the opportunity to BLAST at your fish. If reducing the number of fish is your goal, you would be best to start trapping them and relocating them to the freezer/fryer. Killing the pond would certainly be an option, but I don't know enough about that to advise on the effects of human swimmers. I guess you would have to decide which world you want at your pond, swimming or fishing? And how soon could you swim in it after poisoning the water? Check into the 4 leaf clover fish traps, I have read many accolades for that design for catching pan fish. Reducing the number of fish should reduce the bites, but will not eliminate it I suspect. Eliminating the fish WILL eliminate the bites.

Fish on!,
Noel