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Feeding Koi and Goldfish

The fundamentals of feeding koi and goldfish.

By Stephen M. Meyer

Page 3 of 3

The Feeding Process
There are several factors that influence the appropriate frequency for feeding pond fish. Physiology, water temperature, the availability of natural foods in the pond, prepared food characteristics and fish load are probably the most important.

How Much Food?
The amount of food required to keep koi and goldfish healthy — assuming that the food has the nutritional characteristics already described — depends on two main factors: the age of the fish and the water temperature. Table III offers some rules of thumb for the total daily feeding requirement. It is intended to be a basic guideline — not a hard law of biology.

For example, a 12-inch, three-year-old koi might weigh 400 grams. During the summer, therefore, it should be fed roughly 4 grams of food (dry weight) daily. If, as discussed below, you break the feedings up into four offerings per day, then each offering will be one-fourth of this total daily ration: 1 gram.

The quantity of food should be reduced when water temperatures significantly exceed 78 degrees Fahrenheit for an extended period of time. In most instances the fish will let you know by not consuming all of the food. Uneaten food should be removed immediately after allowing five minutes of feeding time.

Calculating The Amount Of Food
The guidelines presented in this article are just that — guidelines. They can help you determine whether your feeding practices are reasonable. There are three things you need to know in figuring out the correct amount of food for each fish: 1) the age of the fish, 2) its mass, which is related to its length and 3) the amount of food as a percentage of the fish's mass.

Consider, for example, a pond that holds five one-year-old koi and three four-year-old koi. Suppose the one-year-old koi are about 5 inches long and the four-year-old koi are about 10 inches long. It is summer time and the pond water temperature is 72 degrees Fahrenheit.

We can estimate that a 5-inch fish weighs about 22 grams and a 10-inch fish weighs about 200 grams. Based on age, weight and water temperature (see Table III), each of the one-year olds should receive about 2 percent of its body weight as food per day, which is 0.44 grams (440 milligrams). Each of the four-year olds should receive about 1 percent per day, which is 2 grams of food. All totalled, the fish should be fed (5 x 0.44 =) 2.2 grams plus (3 x 2 =) 6 grams, which is 8.2 grams of base food per day.

Now, if we are feeding our fish four times daily, then each feeding would require about 2.15 grams for all the fish. It may be that the fish eat more in the afternoon than in the morning, but on average approximately 7 to 10 grams of food should be consumed per day. If the amount of food you use varies significantly from this, you should re-examine your feeding practices, the health of your fish or both.

How Often to Feed?
From the little that I've said about koi and goldfish physiology, it should be obvious that forcing these pond fish to consume one large meal each day will surely cause a variety of health problems. On the one hand, the more aggressive fish will get all the food, while the more timid fish will slowly suffer from malnutrition. On the other hand, those fish that do ingest large amounts of food will suffer a decline in their abilities to extract nutrients from the food. At the same time, they will be at greater risk of developing intestinal impaction — that is, food jamming in the turns of the intestine. This latter condition leads rapidly to internal aeromonad infections (usually manifested by dropsy).

Optimally, you would like to have a pond setup where the fish could just graze all day long at their own pace. A very lightly stocked garden pond with plenty of edible plants, algae, worms and insects is an ideal aquatic environment. Here, premium pelleted foods may be added as a nutritional supplement or for color enhancement.

In reality, the optimal case is rarely possible, and scheduled feedings are required to maintain adequate diet. As Table III shows, when the water is cold — in the low 50-degree Fahrenheit range or below — the fish should not be fed at all (although they may chose to graze on pond algae). When the water temperatures are in the mid 50- to mid 60-degree Fahrenheit range, two or three feedings that total the daily food ration will suffice.

TABLE III
Total Daily Food Quantity for Koi and Goldfish as a Percentage of Fish Body Mass*

Age
Water Temperature
Below 55 °F 55 - 64 °F 64 - 77 °F
Fry
0

1 - 3%

3 - 5%
Up to 1 year
0 0.5 - 1% 2 - 3%
1 to 3 years
0 0.5 - 1% 1 - 2%
Over 3 years
0 0.5 - 1% 1%
*Percentage of food is for dry weight and assumes correct basic ingredient characteristics
As the water temperature rises into the high 60-degree Fahrenheit range and above, I recommend four and preferably more feedings per day. If there is some natural food in your pond — aquatic plants, small invertebrates and so on — then the total daily ration can be cut, but the number of feedings should stay the same. Remember, you are trying to replicate the continuous feeding process of carp and goldfish, not just the total daily ingestion of food.

I would like to note an important, but sometimes misunderstood, aspect of the well-known "five minute" rule. This rule states: let your fish have all they can eat in five minutes, but no more. The point to remember is that this rule applies to each feeding, not to the total amount of food for the day.

I visited two ponds last summer in which the fish were practically starved to death. In both cases, the owners said they were letting the fish eat all they could for five minutes a day, then removing the leftovers. If you feed your fish only once a day in the middle of the summer, the five minute rule will ensure malnutrition! The proper procedure during the summer would be five feedings, each five minutes long.

Some Final Thoughts
There are several additional points that are important to keep in mind. First, the shelf life of fish food is not infinite, even if it looks and smells okay. In particular, fats and vitamins break down fairly quickly upon exposure to heat and air. The nutrient assay of any fish food pertains only to fresh food, not food that has been lying around the garage for six months.

In general, fish food should always be kept in air- and light-tight containers in cool locations (60 degrees Fahrenheit or less). To ensure freshness, I suggest that you not buy more than a month's requirement at a time. I keep all but enough for one week in cold storage.

Second, unless you have an excellent aeration system and you have precisely measured the dissolved oxygen levels in your backyard pond during the night and morning, you should avoid feeding your pond fish in early morning or late evening. As the plants and algae switch to respiration during the night, dissolved oxygen levels in a pond drop significantly. Fish oxygen requirements increase several times above the normal level during and immediately after feeding. Thus, feeding late in the evening or early in the morning runs the risk that your fish will have an increased need for oxygen at the time when dissolved oxygen is at its lowest levels in the pond. As a guide, I suggest that you not feed until sunlight has been on the pond for at least two hours, and not within two hours of sunset.

Third, water changes represent an important element of proper koi and goldfish nutrition. As noted earlier, they can absorb many essential minerals from the water. As time goes on, however, the dissolved mineral content in the pond water decreases and it must be replenished. If the level of minerals in the water drops too low over time, the fish can actually suffer mineral depletion. (Incidently, this is why keeping fish in distilled water will eventually kill them.)

Lastly, breakfast cereals are not appropriate as either base or supplemental foods. Regardless of what you have read elsewhere, feeding such foods will be appreciated only by your grocer, not your fish.V This article is certainly not the last work on feeding koi and goldfish. I hope, however, it is a good start toward helping you understand the feeding requirements of your pond fish.

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