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Management of Fish in Ornamental Ponds

By Conrad Kleinholz


When you first stock your pond, add only a few fish. Two to five goldfish or 2-3 small koi will allow the biofiltration system to develop properly without toxic ammonia or nitrite levels. The fish will probably be very nervous for the first couple of weeks. You can reduce their stress by adding a place for them to hide. Shade a portion of the pond with a cover, or add plants or some other underwater cover. Avoid rapid movements until the fish are comfortable in your presence, especially if your pond is less than 6’ diameter, since startled fish may panic. They may hit the pond wall at full speed and cause injuries that require treatment.

Within a few days after stocking, the fish should become less wary, and may accept food in your presence. Feed sparingly, no more than 1/4 ration, spread over 2-4 feedings. At this time, you are training the fish to be comfortable while you are there. It is important that the fish eat while you can watch them because refusal of feed is often a sign of stress, illness or injury.

For addition of any subsequent fish you should build or buy a quarantine system. Goldfish and koi are both susceptible to the virus Spring Viremia of Carp. Koi are susceptible to Koi HerpesVirus, and goldfish can be carriers. Goldfish are susceptible to Goldfish Herpes Virus. All fish should be assumed to have parasites which may require treatment before you release the new fish into your pond. To avoid contaminating your pond with diseases, new fish should be held in a separate, secure facility for at least three weeks at the infective temperature for each disease (see Diseases for more information).


Quarantine tanks should be in low-traffic areas of your yard or in an outbuilding. Make sure the facility has a well-operating aeration and biofiltration system and a source of replacement water in case you need to use therapeutic chemicals or medicated diets. A heater may be needed to maintain water at infective temperatures for viral screening, or to increase the temperature for treatment of some parasites. Keep the quarantine area shaded. A net cover will prevent stressed fish from jumping out of the tank. Feed quarantined fish sparingly, ¼ - ½ % body weight, no more than once daily, usually every other day. To maintain bacterial activity in the quarantine biofilter, you can keep an unwanted healthy fish from your pond in the quarantine tank. Remember, this is a one-way transfer.

A quarantine facility also serves as a hospital for treatment of other diseases, parasites or injuries. It can be used to house fish on their way to and from shows, or to be traded, and for rest and recovery areas for fish recovering from spawning. To avoid contamination, all materials used for the quarantine system should be clearly marked and separated from those used in your main pond. This means that filter media, heaters, feed containers and feed, nets, buckets, fish bowls, etc. should be kept completely separate. Wash your hands and arms, feet, etc. with disinfectant wash, or take a shower between sessions at the pond(s) and quarantine facility (ies).

Introduction of Fish to Your Pond

When fish are ready for transfer to the main pond at the end of the quarantine period, make sure the water quality in both locations is similar, particularly temperature, pH and salt content. If not, adjust the water in the quarantine tank over a period of a few days to mimic that in the pond. Use water changes as much as possible, no more than 50% at a time.

Once the water quality is similar in both tank and pond, fill a plastic bag or tub with water from the main pond. Catch the fish from the quarantine tank and place it in the container for transfer to the pond. If you have the quarantine area in a building it may be impractical to maintain the same water temperature as the pond. If so, you can still transfer fish safely. Place the new fish in a plastic bag with water from the quarantine tank. You only need enough water in the bag to cover the fish. Fill the rest of the bag with air from the air pump and seal the bag with a rubber band. Rinse the outside of the bag with clean water, and dry the bag. Place the bag in the main pond and let it float for 15-30 minutes to allow the water temperature to change to that of the pond. Make sure to shade the bag during summer to avoid heating the bag contents. At the end of the temperature equilibration, remove the bag from the pond and place it in a clean bucket or fish tub. Open the bag, remove the fish, and place only the fish in the pond. Don’t put water from the quarantine facility in the pond.

Feeding Your Fish

            Fish, as other animals, must consume foodstuffs to provide them with energy, vitamins and minerals needed for maintenance, growth and reproduction. Fish that receive inadequate amounts of food or its constituents grow poorly or not at all, and often exhibit deformities in the instance of vitamin/mineral shortage. However, unlike mammals and birds, the quality and quantity of food required by fish varies with changes in environmental conditions.

            The nutritional requirements of fish change with size, age and season. Fish are unique in that only a small proportion of species use plant material as their primary food source. Those species, such as tilapia, grass carp and stonerollers, consume nearly their body weight in vegetation daily. Digestion of plant materials by these species is poor. Most fish eat a diet rich in protein and fat. Protein is used for both tissue growth and energy. Therefore, most commercial fish diets contain > 30% protein, and diets for very young fish may contain nearly 60% protein. Commercial diets are partially cooked during production, which increases the digestibility of plant products. The digestibility of plant and animal proteins appears similar in commercial diets, but carp were able to extract more energy from the animal diets (Takeuchi et al 2002).

            Lipids are also an important energy source for fish, and a source of essential fatty acids. The most desirable fats are unsaturated. Unsaturated fats contain less hydrogen, so they are more easily metabolized by the fish. Diets containing high levels of unsaturated fats have a short storage life, because they oxidize and become rancid when exposed to the atmosphere. Rancid diets are unpalatable to fish, so diet intake decreases, which causes an increase in direct loading to the filter system unless feeding rates are decreased. Goldfish do well with diets that contain 3-6% lipids (Sealey et al. 1998). Carp, when given the ability to choose diet ingredients, selected 39% protein, 14% lipids, 21% carbohydrates, and 750 kcalories digestible energy/kg diet (Yamamoto et al 2001). Not surprisingly, chironomid (midge) larvae, the preferred food item of carp, contain 48% protein, 14% lipid, and 23% carbohydrate, with 460-610 kcal/kg dry weight (Cummins & Wuycheck 1971).

            The type and quantity of food required to keep your fish in good health varies with age, size and water temperature. The natural diet of newly hatched goldfish and koi is dominated by zooplankton, such as rotifers and daphnia (Kahn 2003). Zooplankton is a rich source of protein and calories. Protein content of zooplankton varies from 30 – 50% depending on life stage and nutrient availability of their phytoplankton diet (Helland et al. 2003). Guisande and Serrano  (1989) and Vijverberg & Frank (1976) found protein content in zooplankton varied from 50 – 71%. In agreement with these data, larval goldfish were found to grow best on prepared diets containing about 50% protein (Sales & Janssens 2003).

            Small fingerling goldfish and koi grew best on prepared diets containing about 40% protein (Zeitler et al. 1984; Rajan et al. 1996; Bandyopadhyay et al. 2005). As the two species grow to adulthood, their nutritional requirements diverge. Adult goldfish require only 29% protein (Sales & Janssen 2003; Lochmann & Phillips 1994), and they will continue to grow when receiving only 1% body weight of a diet containing 36% protein (Stone et al. 2003). Koi, on the other hand require 30-35% protein, and N excretion was reduced when dietary protein content was 35% (Satoh 1991), indicating more efficient nutrient use with the higher protein diet.

            Commercial diets for goldfish and koi are available in a range of protein percentages. In general, diets with at least 30% protein will yield acceptable growth of your fish. Diet digestibility will vary according to the primary nutrient sources. Goldfish can accommodate up to 70% carbohydrate in the diet (Zhou et al. 2003), while koi have little ability to digest carbohydrates. Since koi don’t digest carbohydrate well (Ellestad et al. 2002), it is important to use the most digestible carbohydrate-based protein sources. Koi digest wheat germ better than corn, and corn better than rice bran (Degani et al. 1997).

Fish have different dietary nutrient requirements based on size, but there are no such restrictions based on water temperature. However, fish metabolism is based on water temperature so the amount of food given to fish should vary accordingly (Table 1). During peak growth periods in late spring and early summer, goldfish and koi can consume about 1.5-2.0 percent of their body weight as dry feed each day.

Table 1. Recommended quantities of commercial fish

diets for goldfish and koi at various water temperatures.

 As the water cools in fall, fish appetite also decreases. For each ten degree Centigrade or 18 degree Fahrenheit decrease in temperature, dietary intake should be reduced by 50%. By winter, your fish should receive only 8-10% of the amount of feed they got during the summer. Remember, also, that what the fish could digest in 10 hours during the summer will take up to 100 hours during winter, so in addition to reducing the volume of feed, reduce the frequency. A few morsels once or twice a week will keep the fish healthy. Some people recommend that fish not be fed when water temperatures decline below 50o F, but fish that do not receive feed during the winter lose weight and are more susceptible to springtime diseases compared to fish that do receive food during winter. However, if you can’t or don’t operate your filtration system during the winter, do not feed the fish until the filter is restarted. Remember that a restarted filter will take the same time for optimal operation as a new filter, so full feeding of the fish will be delayed accordingly.

Since goldfish and koi are ornamental fish and valued for their coloration, size and fin development, manufacturers of prepared diets developed color-enhancing formulas to promote brilliant colors in the fish. Color enhancing diets do work, but their effectiveness varies with variety of fish, fish age and genetics. Development of red coloration in oranda goldfish was enhanced by feeding diets containing astaxanthin, lutein and zeaxanthin for 20 weeks  (Wallat et al. 2005). Regardless of the diet you choose for your fish, be careful that at least 90% of the diet is commercially formulated specifically for fish. Other items can be offered as treats or for some variety, but do not rely on them for nutritional proposes. For example, diets based on silkworm pupae give rise to spontaneous diabetes in koi (Yokote 1974). Water quality and temperature can also affect the color of fish. Coloration is often intensified in cool, clear water, and during spawning season in the spring.

Handling Fish

            Nets for ornamental fish are much different than those commonly found in aquarium or sporting goods stores. Both koi and goldfish have barbed spines in their dorsal and anal fins. The spines can become tangled in nets. The fish can also lose scales and tear fins if the nets are not appropriate. Nets for handling koi and goldfish should have soft mesh, either very fine or large enough that spines will not be tangled. Do not use nets with  knotted mesh. Special koi nets are round, with very shallow bowls, rather than bags. The nets are used only for fish capture, and are not suitable for transporting the fish. The fish are best transferred from the net to a bowl or bag for removal from the pond.

            Both goldfish and koi become accustomed to handling if it doesn’t injure them, so they should become less excited the more times they are handled. When you need to handle them, make slow, deliberate movements, rather than trying to move the net as fast as they can swim. Try not to trap the fish against a hard surface as it may injure the fish. The first few times you catch koi, they will jump from the net if they are frightened. It is best to keep them from becoming excited to avoid the frustration of recapturing them and to avoid the potential for injury to the fish from jumping into the pond edging or the ground around the pond.

            When goldfish or koi, are captured, they are best handled with clean hands rather than moving them in a net. Wet your hands before you touch the fish to avoid damage to their skin. To lift the fish, place one hand under the fish’s head and the other beneath the belly. Don’t squeeze the fish or they will thrash to avoid the pressure. Smoothly lift the fish and transfer it to a bowl for transport. An excellent alternative is to guide the fish into a large plastic bag directly from the capture net. Then simply pick up both ends of the bag and transfer the fish as needed. You can also use a ‘sock’ net to move larger fish. A sock net consists of a short handle supporting a hoop of 8-12” diameter. An open cylinder of very fine, soft material is attached to the net hoop. A fish  is directed into the sock, and the open end is secured by hand. To release the fish, place the net in the water, open the closed end of the net, and allow the fish to swim out of the net.


Literature Cited

 Bandyopadhyay, P, SK Swain & S Mishra. 2005. Growth and dietary utilization in goldfish (Carassius auratus Linn.) fed diets formulated with various local agro-produces. Bioresource Technology 96:731-740. 

Cummins & Wuycheck. 1971. Cited by Takeshi, M. 1995. Production Ecology. pp 269-296. In: The chironomidae: Biology and ecology of non-biting midges. PD Armitage, PS Cranston & LCV Pinder, eds. Chapman & Hall. 

Degani G, Y Yehuda, S Viola & G Degani. 1997. The digestibility of nutrient sources for common carp, Cyprinus carpio Linnaeus. Aquaculture Research 28:575-580. 

Ellestad, LE, R Angel & JH Soares, Jr. 2002. Intestinal phytase II: A comparison of activity and in vivo phytate hydrolysis in three teleost species with differing digestive strategies. Fish Physiology Biochemistry 26:259-273. 

Guisande, C & L Serrano. 1989. Analysis of protein, carbohydrate and lipid in rotifers. Hydrobiologia. 186-187:339-346. 

Hellend, S, BF Sterjisen & L Berg. 2003. Free amino acid and protein content in the planktonic copepod Temora longicornis compared to Artemia franciscana. Aquaculture 215: 213-228. 

Kahn, TA.2003. Dietary studies on exotic carp (Cyprinus carpio L.) from two lakes of western Victoria, Australia. Aquat. Sci. 65:272-286.

 Lochmann, RT & H Phillips. 1994. Dietary protein requirement of juvenile golden shiners (Notemigonus crysoleucas) and goldfish (Carassius auratus) in aquaria. Aquaculture 128:277-285.

 Rajan, MR, P Neelaveni & T Danial. 1996. Feed utilization and growth of ornamental fish koi carp Cyprinus carpio var koi in relation to different protein levels. Environment & Ecoloby 14: 876-882.

 Sales, J & GPJ Janssens. 2003. Nutrient requirements of ornamental fish. Aquat. Living Resources 16:533-540.

 Satoh, S. 1991. Common carp, Cyprinus carpio. In: handbook of nutrient requirements of finfish. CRC Press.

 Sealey, WM, DE Barziza, JT Davis & DM Gatlin III. 1998. Dietary protein and lipid requirements of golden shiners and goldfish. USDA Southern Regional Aquaculture Center. Publication 124.

 Stone, N, E McNulty & E Park. 2003. The effect of stocking and feeding rates on growth and production of feeder goldfish in pools. N American J Aquaculture 65:82-90. 

Takeuchi, T, S Satoh & V.Kiron. 2002. Common carp, Cyprinus carpio. Pp 245-261. In: Nutrient requirements and feeding of finfish for aquaculture. Webster, CS & C Lim, eds. CAB International. 

Vijverberg, J & TH H Frank. 1976. The chemical composition and energy content of copepods and cladocerans in relation to their size. Freshwater Biology 6:333-345. 

Wallat, GK, AM Lazur & FA Chapman. 2005. Carotenoids of different types and concentrations in commercial formulated fish diets affect color and its development in the skin of the red oranda variety of goldfish. N. American J. Aquaculture 67:42-51. 

Yamamoto, T, T Shima, H Furuita, M Shiraishi, FJ Sanchez-Vazquez & M Tabata. 2001. Influence of decreasing water temperature and shortening of the light phase on macronutrient self-selection by rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio. Fisheries Science 67:420-429. 

Yokote, M. 1974. Spec. Publ. Japanaese Sea Fish Lab. 67-74. Quoted in Halver, JE. 1989. Fish Nutrition. 1989. Academic Press, Inc. San Diego, CA.

 Zeitler, MH, M Kerchgessner & FJ Schwarz. 1984. Effects of different protein and energy supplies on carcass composition of carp (Cyprinus carpio L.). Aquaculture 36:37-48. 

Zhou, Z, Y Cui, S Xie, X Zhu, W Lei, M Xue & Y Yang. 2003. Effect of feeding frequency on growth, feed utilization, and size variation of juvenile gibel carp (Carassius auratus gibelio). J Applied Ichthyology 19:244-249.




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