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Goldfish in Cattle Troughs

Farmers keep goldfish in their cattle troughs to keep the algae down and keep the tanks clean.

By Stephen M. Meyer

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Q. I'm a city person (although my town is rather small as cities go), and have been amused to listen to the janitor at work telling me about her goldfish all summer. It seems that farmers here have goldfish in their stock tanks to keep the algae down and keep the tanks clean. With the water heaters they have in the tanks for the winter the fish do all right without any extra care.

I don't know how the fish feel about the cattle and other animals drinking the water they are living in. Nevertheless she's been telling me about the baby goldfish that have appeared, so evidently the fish are happy.

Obviously, the fish will be fine in such a tank. But I had never before heard of this practice and wanted to add to the discussion. Any thoughts?

A. Sue, your story is not really hard to believe. In fact, it shows just how hardy goldfish really are under the "right" conditions.

Why do aquarists seem to have so many problems keeping goldfish alive and thriving in small (20 gallon) tanks? Why do pondkeepers have substantially fewer problems with goldfish, but more significant problems with koi? The riddle is answered by your story.

These cattle troughs routinely hold between 150 and 300 gallons of water. Several goldfish are placed in them, and they are never fed. Instead, the goldfish live off of algae growing on the trough walls and insects that fall into the water. They also cannibalize each other and eat their own eggs.

Underfed and under-populated, they produce little ammonia. What ammonia they do produce is detoxified easily by nitrifying bacteria that populate the tank walls. These cattle troughs reach a comfortable and sustainable biological equilibrium.

So, the secret of success here is fish load control and feeding management. A low fish mass-to-water volume ratio and low levels of feeding produce healthy and stable fish populations in these cattle troughs. Six goldfish in 300 gallons is equivalent to one goldfish in a 55-gallon aquarium. Now, who do you know who stocks a goldfish tank like that?

Over the years I've received numerous letters from readers taking me to task for unrealistic recommendations for stocking goldfish tanks. In most cases these people simply don't understand that goldfish are massive fish for their length, that they need water high in dissolved oxygen, and that they produce significant amounts of waste, making modest stocking densities essential if good water quality is going to be maintained in an aquarium.

I typically suggest that a pair of goldfish in a 30-gallon tank is already a little crowded, and that a 55-gallon tank would be even better. Not many goldfish keepers are willing to accept such a recommendation. Most hobbyists also overfeed their fish, adding to the bioload in the tank. The filtration system cannot cope with this, and the water quality deteriorates to the point where the fish are under chronic physical stress and become sick.

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