Once a new garden pond has been planted and the waterlilies and other aquatic plants have been established for four or five weeks, ornamental fish can be introduced. There is no minimum number of fish necessary for a pond, although without any fish at all it will become a nursery for mosquitoes and there will be little chance of controlling aquatic insect pests. Even for the pond-keeper with little interest in ornamental fish, it is prudent to introduce half a dozen merely to control insect life.
The majority of pond-keepers find fish as important as plants, especially those who have a young family. Children love fish, although there is a danger of over-stocking, for there never seems to be enough in any pond for young children. There is also impatience to get the new pond stocked immediately it is filled with water. This must be resisted until the plants have had an opportunity to establish. While there is no minimum requirement for fish, there is a maximum number that should not be exceeded.
The most satisfactory stocking rate is the 2ins length of fish to every 1 square foot of surface area. This is not of the total surface area of the pond but of open water uncluttered by marginal plants. This rate of stocking permits growth and development of the fish and makes natural breeding likely. Fish enthusiasts will often stock more heavily than this, but an absolute maximum is 6ins to every 1 square foot of surface area.
When purchasing fish a good guide as to whether they are healthy is the condition of their fins. Stout upright dorsal fins and well-expanded ventral fins are an indication of good health and this can be confirmed if the eyes are clear and bright as well. An obvious consideration when selecting fish is their liveliness. However, while a lively fish is likely to be a healthy fish, it could equally be a very hungry fish. It is common practice with many fish retailers to keep the fish a little hungry. This ensures that they swim and dart about the tank in search of morsels of food and therefore appear livelier than they would ordinarily. An added bonus is the reduction in the fouling in the tank.
With small fish it is important to see that there are no damaged or missing scales as exposed tissue is very susceptible to fungal infection. The same applies to larger specimens, although it is not so critical, and the likelihood of finding a large fish that has no scales missing is fairly remote. If an otherwise healthy fish has a few scales missing, then dip it in a proprietary fungus cure. It is prudent in any event to treat all newly purchased fish in this way as a precaution before introducing them to the pond.