Pond fish provide a natural filter and contribute to the overall health of your pond. Goldfish and Koi are the most popular pond fish because their colors are greatly visible underwater. When choosing to stock your garden pond with either Koi or goldfish consider that Koi require a larger pond then goldfish because they continue to grow despite the size of the pond. Also, overstocking a fish pond can be a costly mistake. Too many fish (especially Koi) can rob one another of essential oxygen. Feeder goldfish should always be the first additions to a pond. However, keep in mind that pond water should develop for several weeks before any fish are introduced.