3. Choosing Fish

The biggest mistake small ponders make is overstocking. My local pond store surveyed the size of everyone’s ponds and the number of fish and said overwhelmingly his customers had too many fish. Way too many

First off – in a pond of 500 gallons or fewer, one should not have koi. To raise koi properly, one needs 1000 gallons minimum for swimming room and then 100-200 gallons per additional fish. They will grow to an adult size of two and half feet or more, and there is no way to stop them without making them sick. A lot of people like to raise koi in a small pond and then transfer them when they outgrow the space, but I can tell you from experience that it is financially unwise and potentially disruptive to the health of both your pond and the koi. Everyone wants to have the jewel-like koi in their ponds, and KOIUSA created a furor when they published an article on raising young koi in an 85-gallon pond, but it is not practical. Hanover Koi Farms is trying to breed “toy” or “bonsai” koi that will only grow to goldfish size (12-14 inches), but they have only a limited number available each spring.

Goldfish fit the small pond better. They do not grow as large as their cousins the koi, and they grow more slowly in smaller ponds. Goldfish, like other animals, may vary in size even within varieties. Most max out at 8-10 inches, but goldfish over a foot long are not that rare.

Determining how many fish to put in a given pond takes some calculation. Veteran ponders can look at your pond and spot overstocking instinctively. Like the justice who once said he could not define obscenity but he knew it when he saw it, pond experts can assess stocking levels instantly, but when pressed for formulas, they throw out suspect or unscientific ones. Many times they give you a rule of thumb based on inches of fish per square foot of surface area or per gallon of volume. The stress that fish place on a pond system is proportional to the weight of the fish, not the length, however, and weight increases exponentially with length. Inches, therefore, are not relevant. Filtration and weight are. This weight chart from Russell’s illustrates the relationship between length and weight:

Fish Length Weight in Ounces Weight in Grams
1″ .01 .28
2″ .08 2.27
3″ .26 7.37
4″ .62 17.58
5″ 1.21 34.30
6″ 2.09 59.25
7″ 3.33 94.40
8″ 4.96 140.61
9″ 7.07 200.43
10″ 9.70 274.99
12″ 16.76 475.14
14″ 26.61 754.38
16″ 39.72 1,126.04
18″ 56.55 1,603.17
20″ 77.58 2,199.36
22″ 103.25 2,927.10
24″ 134.05 3,800.25
26″ 170.43 4,831.61
28″ 212.87 6,034.76
30″ 261.82 7,422.47

[Fish are measured from the mouth to the peduncle, or junction of the body and tail]

To make a reasoned calculation of the amount of fish that a pond could support, one would need to know the cycling capacity of one’s filter and the total mass of fish. Water volume also plays a role. If you have a calculator, more information than most filter makers will give you, and more time than sense, you can use tables to calculate exactly the amount of fish you pond will support.

As a practical matter, I have created a rule of thumb from their various numbers. If you use a recommended filter and pump for your pond, you should be able to support 3 grams of goldfish for every gallon of water. Start below that load and see whether your pond continues to maintain good water quality as the fish grow. You may have enough filter capacity to support more poundage, but it is never a good idea to start a pond with too much stock. If you insist on eventually loading the pond as full as possible, start with a manageable load and work up.

Choose fish for your pond that are pond fish. Fancy goldfish cannot take the rigors of the pond and need to be brought indoors during the winter, so avoid them, as changing their environment twice a year will shorten their lives.

Goldfish that thrive in ponds include:

1. Hibuna or common goldfish – Commons, often referred to as feeder fish, are pond-hardy and usually inexpensive, though prize quality fish can fetch a high price. Because of their low cost, some hobbyists treat them as disposable, but in a pond environment they can grow large and impressive. They come in red, white,and gold; some sport black when young.


2. Comets – Slender goldfish coming mostly in red. Tail is more pronounced than in Hibuna, hence the name. Sarassa comets have the koi-like red and white patterns pictured below.


3. Shubunkins – Calico (multi-colored) goldfish with a body shaped like the comet. Because of their varied patterns and colors, they are often called “poor man’s koi.” The British have bred the London and Bristol varieties, which sport elaborate fins.


4. Wakins – These are common Japanese goldfish but relatively rare in the US, though they have been gaining popularity. They boast a distinctive fan shaped tail. Mostly red and white, calico wakins have been bred, as well.


5. Jikins – Bred from wakins, these goldfish have a “four-leaf clover” tail. The most prized have all red fins and a white body, sometimes achieved by removing non-white scales. Expensive but impressive.


6. Watonai – A cross between the Wakin and the Ryukin, its double tail spreads wider. These have appeared more often in goldfish literature than in tanks and ponds in recent decades, but several breeders have recently revived this hybrid. The fins display nicely in the pond.


7. Tamasaba or Sabao – These consist of a single-tailed variant of Ryukin that resists cold well enough to overwinter outdoors. They are rare in the United States and prized by those who raise fish for show. Since most of them come from conservative breeders in Japan, they are almost exclusively red and white in color.


Then there are Toy or Bonsai Koi. Hard to find, harder to believe, these are supposed to stay small, only growing to a foot or so. If you go this route, buy only koi specially bred to stay small from a reputable fishery. Many small koi are simply stunted – they are unhealthy and have been kept in crowded, cruel conditions, even small aquaria. Like puppies bought from a puppy mill, there can be nasty surprises down the road. Stunted koi can suddenly start growing and become grotesque, or, worse, their malformed organs and compromised immune systems make them incubators for disease.

Bitterlings can also be put in a pond with goldfish. They are hardy and tough. Plecos will not winter and grow quite large eating the muck, so only add one if you are in an extremely warm climate.

If possible, buy your fish from a pond dealer that you know quarantines fish for an extended period of time. If you buy your fish from an aquarium supply store that has many indoor tanks running off a handful of water supplies, you will need to quarantine any new fish yourself. For that reason and others, it is best to avoid big box pet supply chain store outfits. Levels of expertise and fish care vary widely from store to store, and often the staff cannot answer your basic questions.

When picking out particular fish, you should look for a healthy amount of activity, a lack of damage and disease, and good form. In terms of activity, choose a goldfish that swims energetically and with curiosity. Avoid fish that do not move about or socialize with others. Look for intact finnage and the absence of sores, lumps, and blemishes.

Steve Hopkins of Rain Garden Ornamentals gives the following basic advice for selecting well bred fish:

If you want a hibuna, shubunkin, comet, wakin or watonai that has the potential to grow large, look for: 1) A long nose (a long distance between the tip of snout and eye). This means it has the genetic potential. And…

2) A rounded back when seen head-on. If the dorsal fin area has sort of a ridge or peak, it means the fish has not been fed well. The first place a fish looses weight is the muscle along either side of the dorsal. Once underfed for any length of time, it can never catch up with it’s genetic potential.

If possible, you should always quarantine new arrivals, but many people with small ponds do not have room or money to set up a separate tank. Folks with large ponds often have a quarantine tub larger than most small ponds! Floating a small tub will give you a quick and dirty quarantine tank, but water quality must be monitored constantly under those conditions. If you cannot or do not want to go to the trouble of isolating the new fish, buy from a dedicated pond fish dealer and only after determining that the fish were properly quarantined and are fresh out of isolation.

Sometimes the only way to find rare or exotic goldfish is via mail order. Having fish shipped to you is expensive and risky, but there are many reputable dealers who trade this way. Consult other ponders via internet forums or your local club to verify the reputation of anyone you might buy from. Be especially careful of eBay traders. I have heard too many horror stories about fish bought via their auctions.

The number of patterns and colors available in pond-hardy goldfish far exceeds most folk’s expectations. A pond of variegated shubunkins, elegant wakins, quick swimming comets, and exotic jikins can be almost as visually interesting as one full of koi.

Choose fish you like, and catch them yourself if the dealer allows. Examine the fish in your hand for wounds or infections, and make sure it feels slimy in your hand – that is the fish’s natural layer of protection. When you transfer your new boys and girls from bag to tank or pond, use your hand not a net. It will stress the fish less and carries far less risk of injury. Likewise, try to catch fish in a plastic container instead of a net, if it is practical. If you must use a net, try not to chase the fish too much, as it will upset them.


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