Big Fish, Little Fish
By Miller Morgan

For many pond keepers, fish play an essential part of the pond experience. Although a variety of species can be kept in ornamental ponds, koi and goldfish remain very much the fish of choice. Because it can be rather expensive to buy adult fish, the vast majority of pond owners purchase juveniles. Given time to grow, these coolwater fish become big in length and overall size. What was an understocked pond when the fish were young can become overstocked as the fish grow and the bioload increases.

Knowledgeable hobbyists stock lightly to begin with or remove individual fish to keep a biological balance in the pond. Ornamental ponds typically have a much higher bioload of fish than natural ponds, but these efforts to maintain a healthy environment can be complicated when the maturing fish are ready to make little fish. At first, having your fish breed seems like a wonderful thing, but absence of natural predators to reduce the multitude of young fish leads to an overcrowded pond.

Breeding pond fish requires little skill on the part of the pond keeper. When water quality is good and food nutritious, koi and goldfish breed. Unless there’s only a few fish, the odds are you will have a mix of males and females. Several males pursue a female, guaranteeing future generations.

When Fish Multiply
When you see small versions of the adults, decide your course of action. Well-fed adults eat young only by accident, and this occurs only when they are under an inch in size. There’s a good chance you will end up with far more fish than you want, with one caveat: fish eggs. Fish eggs are popular food options for a variety of wildlife. You might not have many small fish to deal with, but there’s a good chance you will have at least some. While free fish might seem like a good thing, there are two concerns.

First, there are distinct limits to how many fish the pond can hold safely. The larger the fish, the fewer there can be. Second, even if you have high quality koi in terms of pattern and color, many of the young will not exhibit these qualities. You will want to remove the young that show the least desirable in terms of appearance.

Also, koi and goldfish change pattern and color with age. Some improve in color and/or pattern, but others might lose their quality. This is why quality koi and goldfish cost a pretty penny. Professional breeders have to know which adults are most likely to have more desirable fry and then hand-breed them, and they also have to cull the young, keeping only the very finest that conform to traditional standards for color and pattern.

If up to this task, you could cull weekly. This simultaneously reduces the bioload while removing unwanted fish. If this seems cruel and inhumane, keep in mind that fish produce many eggs and young because predation, genetic issues, a lack of sufficient food and disease will result in a very tiny percentage reaching adulthood.

Overstocked Pond
What to do with all the young? You can give them to other hobbyists who have room for juveniles to grow into adults. You might work with aquarium stores or koi/goldfish retailers, in which you receive credit for food and supplies. Unless the fish are of sufficiently high-quality, however, it’s unlikely that dealers will be interested. Other pond keepers also might attempt to find ways to dispose of their young fish, which means there will be competition.

Speaking of disposing, euthanasia offers an alternative. You can accomplish this in a number of ways. The most humane is to place fish in a small container — just enough water to cover them — and put this container in the freezer. As the water becomes colder, the fish will become unconscious and then freeze to death.

Do not flush fish down a toilet. These fish will suffer slow death as the water becomes increasingly polluted in sewer pipes leading to a waste water treatment facility.

If you want to raise some of the young in a pond or very large aquarium of 300 gallons or more, the main issue is food. A pond that has been running for many months should have a variety of organisms on surfaces and the bottom as well as vegetable matter — certain forms of algae and other tiny plants — that the young fish can eat. The food pellets for the adults will be much too large for the growing youngsters, but you can feed very small pellets meant for koi and goldfish several times a day. Pellets meant for other kinds of fish will not have sufficient vegetable content for koi and goldfish.

In nature, fish breed in the spring or rainy season when food is more abundant. Ponds in areas with freezing temperatures and ice will take two or three months to warm in the spring and become biologically active enough to produce algae for the young fish. <HOME>

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