Q. When I completed my 1700 gallon pond about six years ago I stocked it with a dozen — presumably sacrificial — goldfish from K-Mart. They cost 22 cents apiece. Thus, my investment was small in the event that chlorine and chloramine were not adequately dissipated.

Well, they did just fine. In fact, they bred and bred until they numbered close to 100! Giveaways and a frog invasion reduced their number, and I now have added three koi. All are kept in the pond year round. But now I come to the point.

Three of the goldfish have developed cysts that have grown over a period of months. I hope the enclosed photos may aid in identification. Can you tell me anything about the cause, prevention or treatment?

A. The pictures were very helpful. The cauliflower-like cysts erupting through the surface of their skin is the classic sign of Lymphocystis disease. This disease is caused by a virus that infects connective tissues throughout the body. The disease progresses slowly and is usually not fatal. It is very unsightly, however, and ruins the appearance of ornamental fish.

The virus can be transmitted from fish to fish. Ruptured cells shed the virus into the water. Breaks and openings in a fish's outer skin and slime layer provide entry. About a month lag occurs between initial infection and first signs of the tell-tale cauliflower growth.

There is some evidence that infection is much more likely among fish that stay near the bottom of aquariums and ponds. This is because the infected cells shed by host fish are heavy and drift downward. Goldfish, being bottom scavengers (as are koi), are therefore likely to encounter the virus in a closed system.

There is no treatment, and you must assume all the fish the pond are infected. You can limit the impact of the disease by 1) removing all fish with lymphocystic growths and 2) significantly reducing the fish population in the pond.

Alternatively, you can sacrifice all the animals in the pond. Drain it and disinfect with chlorine, refill and let the pond sit fishless for several months. When you go to add new fish you should quarantine them for a month in a holding tank with water temperatures above 70 degrees Fahrenheit. You should see some signs of the disease within two weeks. Nevertheless, wait the full month. There is no doubt that the infecting virus entered your pond when you added new fish.

In Zone Five
Q. I am interested in building a 4-foot by 6-foot pond for koi. I live in Zone 5. Can you advise me on construction regarding the appropriate depth, material, pump, filtration and winterizing? I am very fond of koi. Can they survive a Michigan winter?

A. Your letter was short and simple, but a complete answer would take up the entire magazine. The one piece of advice I will offer is that your pond is far too small to properly raise all but the smallest koi. If you truly appreciate koi and want to enjoy the pleasure of watching these animals grow and develop to their full potential, then you need to think about a pond that is at least 16 feet long and 12 feet wide (approaching 200 square feet of surface area). I think this the minimum to raise a pair of koi under optimal conditions. Good biological filtration will give you some extra capacity, but not enough for several more fish. If the 4-foot by 6-foot footprint is dictated by space constraints, then I suggest you think in terms some of the smaller varieties of fancy goldfish.

Koi are not coldwater fish. And even if they survive a string of Michigan-like winters, they do not endure them well. Moreover, as the fish grow larger the risks of death increase. With this in mind I suggest a deep area running to four or five feet (assuming my recommendation for increased surface area is followed). The surface will have to be kept open with one or more deicers.

You might try to find a goldfish or pond society in your area. They will have first-hand experience with pond conditions in your area.

That New Tank Problem
Q. I've been keeping varieties of goldfish for many years — my first one lived eight years by himself in an unfiltered 5-1/2 gallon tank with biweekly complete water changes. Since then I have learned an enormous amount about goldfish. One problem, however, still plagues me — avoiding "new tank syndrome."

I recently purchased four small bubble eyes for a 20-gallon tank. After only three days one fish died from dropsy. A week and a half later another showed signs of finrot.

The ammonia levels are only slightly raised, and I keep doing 25 to 50-percent water changes weekly. Your help would be greatly appreciated.

A. You have several things to consider. New tank syndrome occurs when aquariums or ponds are set up for the first time — it's a water quality problem. Lacking an established colony of nitrifying bacteria, ammonia levels in the water rise to toxic levels. As the nitrification process takes hold, nitrite (an even more toxic substance) concentrations also rise The process of establishing effective nitrification takes four to six weeks, and deaths usually being after the first week or two.

This is easily avoided. All you need to do is set up a new tank without fish, start the filter, add several parts per million of ordinary household ammonia every other day for four weeks, and you will have established a healthy population of nitrifying bacteria.

Test the water every couple of days. You will see ammonia and nitrite levels rise and fall. When they stabilize near zero (after about a month) you can add fish.

I doubt, however, that this is your problem. The fish load was too small for the volume of water to produce ammonia poisoning. Did you test your water for chlorine and chloramine? If it was present did you neutralize these agents?

You should also compare the pH in your tap water with that from the aquarium store. It sounds much more like severe water quality stress depressed the fishes' natural defenses.