Fish Facts

  • How many fish do I need for my water garden?

    Stock fish, in a new pond, at the rate of one inch of fish for every five to eight gallons of water. (Fish are measured from the tip of the mouth to the tip of the tail.) This low stocking rate allows growth and reproduction. Stock lightly in a new water garden so the fish waste doesn’t overwhelm the bacteria that removes the waste from the water. A mature pond can support an inch of fish for every two gallons of water.

  • Do fish grow in relation to the size of the pond?

    Heavily stocked fish tend to grow slower in a water garden, but will eventually become large, regardless of the size of the pond. It may take longer for a fish to become large if it is crowded, due to competition for food. Large fish have been observed in small ponds. They may be older than similar size fish in a larger pond.

  • Can I mix koi and goldfish in the same pond?

    Goldfish and koi are compatible in the same water garden. Because koi get so much larger, they are often kept in a separate pond from goldfish, but they do not have to be. Koi are sometimes separated because they can be disruptive to plant life by digging up plants and eating their leaves and roots.

  • Do I need to feed my fish?

    Goldfish that are fed regularly will be more active and visible. If they are not fed, they will be very shy, not coming out into open water very often. They can survive with no additional food, subsisting on algae, insects and other organic matter. Feeding with floating pellet foods keeps the fish coming to the surface and learning that when they see people, that it means food. Color enhancing foods can be useful in increasing the color intensity of the fish.

  • How much do I feed?

    Feed fish only what they can consume in about five minutes per feeding. They can be fed two or three times daily if desired (or not at all if you wish). If uneaten food is left floating on the pond it fouls the water by leaching out nutrients that feed algae. If the fish do not eat the food, net it off immediately. If the fish are fed too much, the water will become fouled either from food that remains uneaten, or from excess fish waste from overeating. Some gardeners increase the use of filtration in order to feed fish more. Use a larger filter, or a more efficient one, along with beneficial bacteria to be able to feed fish more than normal.

  • When do fish spawn?

    In the temperate United States (Zone 5, 6, & 7) goldfish spawn in May and June. Spawning is recognized by vigorous splashing along the edge of the water and relentless chasing of the female fish by the males. The eggs are deposited on underwater plant surfaces, then fertilized by the males. They will hatch in a couple of weeks but the adult fish often eats the young fish (or fry). If you want to keep the fish that spawn, be careful to protect the eggs when you see them. They look like pin head size clear beads that are stuck to underwater surfaces. Usually underwater plants and roots of floating tropical plants (like water hyacinth and lettuce) provide sufficient cover for many of the babies to find shelter. If all fry lived through the earliest stage of growth, you would soon be overpopulated with goldfish. Natural selection reduces the less vigorous young.

  • How do you tell a male from a female fish?

    You can tell the sex of goldfish during the spawning season by looking closely at the fish while they are swimming around, however, this is easier said than done when the fish are in constant motion. The fish should be four or five inches in length before you can identify males and females. During May and June the adult female fish will usually have a wider than normal body shape. They get significantly larger because they are filled with eggs. The male will remain much sleeker and will display what appears to be salt grains on the gill covers. The male will chase the female, so that means the lead fish is the female and the ones chasing her are the males. There are many more males than female in the average pond, but with the hundreds of eggs laid during spawning, some fish should survive to become adults.

  • How big will my fish grow?

    Comet goldfish, the most common variety, will reach 8-15″ at maturity. These fish will reach nearly their full size, then begin growing more slowly. Their bodies grow less, while their fins continue to grow, becoming more flowing. They can live twenty years or more. Shubunkin goldfish grow similarly to comet goldfish. Fantail varieties of goldfish grow to a length of 8-10″ and usually live eight to ten years.


    Golden Orfe grow to lengths of fifteen inches or larger very rapidly. It is not unusual for a Golden Orfe to grow from three inches to ten in a single season. They grow more rapidly the first year or two than later years. This variety of fish will live for ten years or more.


    Koi, Domestic or Butterfly, will grow to a length of 18-36″ long. They grow rapidly when adequately fed and where they have plenty of room to grow. A well cared for fish can live well over a hundred years.

  • Do I feed my fish in the winter?

    Fish are not fed at all when the water temperatures drop below 45 degrees. They cannot digest well when temperatures are low. The food will foul the water because the fish will ignore it. When the water is between 45 and 55 degrees, they will eat and can digest foods made primarily with wheat germ. Use only wheat germ foods during cold weather or discontinue feeding altogether.

  • Why do fish gasp at the top of the water?

    Fish gasping at the surface indicates a low oxygen level in the water. This is caused by rapid decomposition of organic matter in the water. When a treatment is applied to the water, the oxygen levels drop temporarily because organic matter dies as a result of the treatment. All water treatments must be applied early in the day so the water can recover from oxygen depletion. Treatments late in the day or evening remove oxygen that can not be replaced by normal plant respiration.


    Gasping fish need the water to be agitated or oxygenated quickly. A pump gurgling to the surface makes a very efficient oxygenation system. A pump connected to a fountainhead breaks the water into tiny droplets that put oxygen back into the water as well. For a quick temporary fix is to set up an aquarium air pump and air stone to put air bubbles into the water.

  • Will fertilizer hurt my fish?

    Fertilizer for aquatic plants is formulated to be safe for fish and other creatures of the water garden. The tablets are inserted into the soil, then covered, so nutrients are not released into the water. Even if nutrients are put into the water, they make algae grow with no other ill effects.

  • Why are fish chasing each other around the pond?

    With the female fish in the lead, the males are chasing her in the annual spring ritual of spawning. The relentless chase may last three or more weeks until spawning has taken place. The males are waiting for the female to lay her eggs on an underwater plant so they can fertilize them.

  • Why do the fish look like they are attacking a fish in the shallow part of my water garden?

    During the spawning season, it may seem as if some fish are attacking one or more fish in the pond. The males will chase the females around the water garden even into the shallow parts pond’s edge. They may end up on top of potted bog plants or even occasionally splashing all the way out of the pond. There is no harm to the fish unless the female is weakened for some reason and the spawning ritual could cause death. While this is rare, it has been observed.

  • Do koi eat plants?

    Koi eat plants including water lilies and bog plants. They eat any vegetation that is in the water. While a koi is small (up to 6 or 7 inches), they do not cause much trouble for plant life. Once they begin to get larger, they can be devastating, devouring plants and muddying the water by constantly rooting around the pots of soil. Use a submerged plant protector or screening to provide a barrier between fish and plants. It is often advised to provide a separate pond for koi, keeping them totally apart from the plants.

  • How big will koi get?

    Koi can easily attain a length of 24-36 inches if enough room is provided along with ample food. The large koi will also increase in girth as their body lengthens.

  • Why do my fish have large open sores on their bodies?

    Open sores or large pimple-like lesions on the side of a fish are often a result of Ulcer Disease. This contagious and often fatal disease is difficult to control and needs aggressive treatment. Fish that are under environmental stress or are living in poor quality water have a good chance of contracting the disease. Correcting the water quality issues and treating with a product such as Melafix will likely take care of the problem.

  • My fish have what appears to be salt grain on their fins and body, what are these?

    A cold water parasite called White Spot or ICH is responsible for what appear to be salt grains on the body and fins of a fish. An advanced case where the body is largely covered is often fatal. Early detection and treatment is imperative. The fish will hang near the surface of the water and act disinterested in food and other fish. This parasite lives in the silt and debris layer of the bottom of the pond and even on the body of a healthy fish. When stresses occur, like a sudden drop in temperature, the parasite becomes free swimming and will attach itself to the fish. Treatment with an ICH control medication that contains formaldehyde and malachite green is needed to eradicate the parasite.

  • My fish have cottony stuff on their bodies and fins, what should I do?

    A fuzzy film on the fish is an indication of an injury, parasite or a water quality concern. A fungus that grows on dead or damaged flesh will appear cottony, almost like bread mold. Get rid of the parasites, take care of water quality and provide a topical healing so the flesh repairs itself. Apply a fungal control medication to eliminate the fungus organism and the problem should disappear soon.

  • My fish have been lethargic, not eating or swimming mush, what does this tell me?

    Slow moving fish that hang (actually drooping) near the surface of the water indicate a potential illness or water quality concern. Look for spots, redness, torn and frayed fins or any symptom that would indicate a health problem. Check the water quality for excess ammonia, nitrites and high pH and take care of what needs to be fixed. Once the water quality is re-established, the fish should be more vigorous and active.

  • I want to grow baby fish, how can I encourage spawning? How do I keep the fry safe from the adults?

    Goldfish can be grown from eggs providing they are protected from the adults. In a water garden, the fish spawn on submerged plants where the eggs are deposited, then fertilized. Once they are fertilized, the eggs hatch in a couple of weeks. After hatching, the adult fish eat them if they emerge from hiding in the underwater plants. The plants offer protection for a few fish, but often there will be plenty that survive. If all survive, the pond would soon be overloaded with fish.


    Spawning mats are sheets of latex coated fibers that provide the fish with a spawning media on which to deposit their eggs. The mat must be moved to another pond where there are no adult fish so the eggs can hatch without the fry being consumed.


    One of the best methods is to install a Fish-Spawning Incubator Basket that provides a spawning medium and then a nursery for the young fish. This floating basket is fuzzy on the outside, giving the necessary surface for promoting the release of eggs by the female fish (OK, it tickles her…). Once the eggs are attached to the fuzzy surface, the basket is turned inside out so the fuzzy side is on the inside. The eggs hatch inside the protection of the basket where the adult fish can not get to them. The fry can live in the flow through environment until they are released into the main pond later in the summer.


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