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Feeding Goldfish in Winter

Should you feed goldfish in the winter or not?

By Stephen M. Meyer

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Q. I have heard some conflicting information with feeding goldfish during the winter. Do you feed them or don't you?

Also, my pond is about 10 inches to a foot deep. It does not freeze much here, but should I move my fish to my other pond, which is just a little bit deeper?

A. It's not surprising that you have heard many different things about the advisability of feeding goldfish kept outside during the winter months. If you talk to hobbyists from Louisiana they may tell you how their fish devour food all year round, and may be especially hungry between November and March.

A novice pondkeeper in your own area may confidently state that he or she has never had any problem feeding goldfish during winter. Conversely, if you talk to hobbyists from Wisconsin you will hear about how any feeding after October leads to a pond of dead goldfish. If you feed your pond fish after the weather starts to turn colder, they will caution, you will kill your goldfish.

These are not conflicting stories, nor do they imply conflicting advice. All advice about pondkeeping must be evaluated in context. In this instance the critical context is climate: In terms of pondkeeping, what is meant by winter? Winter means different things in different geographic areas.

Winter in Hawaii means a drop in average daily temperatures from 85 degrees Fahrenheit (summer) to 72 degrees (winter). In Maine, winter means a drop in average daily temperatures from 75 to 25 degrees. In any given area some winters will be milder than others, so "winter" is a relative concept when measured in terms of temperatures.

From the perspective of the fish, the single most important consideration is whether feeding is safe or dangerous. It's not the season per se, but the average ambient water temperature that matters. The rate of digestion, as well as other metabolic processes, in fish is set by the body temperature. In turn, a fish's body temperature is set by the water temperature.

Keep in mind that fish do not generate their own body heat by burning calories as mammals do. They depend on water temperature and solar radiation for heating (or cooling). Fish move within waters of different temperature and areas of differing solar illumination to adjust their body temperatures — this is known as thermal regulation. Fish in a pond have very limited opportunities for thermal adjustment.

At some point, depending on the species of fish, the water temperature can get so low that the many mechanical and biochemical functions that make up the process we call digestion effectively stop. The ingested food becomes stuck in the fish. This is known as gut stasis. Extended periods of gut stasis are associated with severe internal bacterial infections in goldfish and koi (as well as certain captive-raised game and food fish).

But even before the point of reaching gut stasis the amount of time that food stays in the digestive tract may be long enough to threaten disease. Food that might pass though a fish in a few hours at 75 degrees may take a week or more at 55 degrees. Many bacteria thrive in this situation and quickly overcome the fish's immune system defenses (which are also barely working at low temperatures).

Temporary temperature fluctuations - such as a several days of cold weather in the late spring — do not pose a threat to pond fish. But the sustained low temperatures the come with the winter season are a real danger.

Therefore, the general advice to stop feeding pond fish when ambient water temperatures drop into the low 50s is quite sound. This is a problem of relative risk. Feeding at 51 degrees is riskier than at 57 degrees. There is no precise cutoff temperature.

Won't the fish starve if you stop feeding them? Not at all. Remember, their entire metabolism slows to a crawl when the ambient temperature drops into the low 50s. Fish need very little energy (calories) at that point.

Regarding pond depth, I find that a foot of depth is just too dangerous. Neighborhood cats, large birds, raccoons, foxes, coyotes and so on can easily fish out a shallow pond.

Should you get a rare hard freeze in your area for a few days, an ice cover could form on the pond. The 10 inches or so below the ice would not give the fish a wide margin of safety in terms of water temperature or available dissolved oxygen.

Then, too, shallow ponds are great solar collectors, and, lacking proper shading, you could find your fish boiled to death one fine summer day. Deeper ponds provide some protection against extreme high temperatures caused by solar illumination.

For these and a host of other pond management reasons, I suggest you drop the depth at least another 6 inches — to 18 inches — in half the pond. And a 24-inch depth would be even better.

Now, I recognize that many prefab pond forms have a maximum depth of 10 inches to a foot. These are fine for water gardens — that is, miniature pools for growing aquatic plants, providing water for birds or bringing a water feature into the landscape. Putting a goldfish or two in for aesthetic reasons can be fun. These pools are really ideal for first-time pond hobbyists who are not yet certain whether the purpose of the "pond" will be plants or fish.

But these shallow pools are not for serious fishkeeping, and they are certainly not appropriate for keeping high quality (read expensive) goldfish or koi. Should you find your pond interests moving toward breeding fish, then it will be time to rebuild the pond to match that goal.

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