Start by knowing how many fish your pond can handle. One general rule is to have 1 inch of fish for every 10 gallons of water. So if your pond has about 50 gallons of water, you can have one 6-inch-long fish, two 3-inch-long fish, or six 1-inch-long fish. If you're not sure how much water your pond holds, it's better to underestimate rather than to have too many.

When purchasing fish, pay attention to the shop's environment. The cleaner the store and the ponds, the more likely it is the shop staff give the fish good care.

Avoid purchasing fish from a tank that has dead fish floating in it. That may be a sign that the fish are unhealthy or diseased. Also pay attention if any of the fish are sick. One common sign of a sick fish is if it hangs out alone and has clamped fins. Unhealthy fish may also be missing scales, bear sores, or have missing fins.