We've had an assortment of disease problems. I'll discuss 3 here; one that turned out to not be a disease, one that is incurable but apparently non-fatal, and one that I am still trying to cure and for which I don't have a good diagnosis. Some brief descriptions follow, along with some very marginal pictures.
We have four ranchu that started getting rather alarming white pimples on their wens (headgrowths) at about 9 months of age. The pimples would come to a white head over about a week, and then leave a raw spot as they healed for a week or so. Turns out that this is not uncommon for headgrowth fish as they go through spurts of development of the wen. For my fish, I found a teaspoon of non-iodized salt per gallon speeded up the healing process. An example picture. (85KB). In general, people that breed headgrowth-type fish seem to consider this a normal part of wen development.
We have an oranda that developed an abnormal, mustard yellow headgrowth. The growth started while we were on vacation in December of 1995. When we returned at the end of the month, the growth was the size and color of a half yellow split pea. Five months later, the growth is 4 or 5 times that size, but appears to have slowed its rate of growth. The fish seems unconcerned and its tank mate, a telescope eye, shows no similar problems. Suggestions on this included to stop feeding Hikari pellets and improve water conditions, both of which I've done. Apparently, headgrowth fish sometimes get these growths, and while unsightly, there is not much to be done. A black and white image of the oranda. (40KB) and a color closeup (33KB). Note the bubbles on the tumor and wen; these have disappeared since the photo was taken. Post et al, in The Manual of Fish Health, discuss a viral agent that can cause this type symptom. It is not treatable, but is also typically not fatal (and may even clear up after a few weeks, though the affected fish is still a carrier). If this is the oranda's problem, it is not clear how it was infected, since it has been with a single tank mate for 3 years. My best guess is that it was either present all along and stress caused an outbreak, or I introduced plants that somehow carried the virus (less likely).
The final problem is a white tail spotting on my ranchu. Only some have it, and it seems to spread very slowly. What I see are 1 to 2 mm white dots on the outside surface of the lower part of the caudal fin. From the sides, you can see a slight raised area on the fin surface. Whatever this is, it is unresponsive to Coppersafe. I've had some success with Nitrofura-G in a hospital tank, but the problem seems to return when the fish is placed back in the main tank. I actually treated the entire tank with Nitrofura-G for one full month. While this reduced the symptoms, it did not eliminate them. A close-up of the tailspot disease. (14 KB) (Update: I believe this is also viral, probably in the lymphocystis family. The fish still have it mildly, but with good water conditions it reduces to just a spot or two. In any event, the fish are thriving a year and half later.)
In general, what I've learned so far is to have a few extra tanks around and to take a close look at the fish each day. Once you find a problem, though, diagnosis is very difficult (short of a lab analysis of the fish) for any but the most obvious diseases. If you decide to treat, particularly with antibiotics, follow the instructions carefully and carry out treatment for the FULL recommended period. These products often take time to work (my experience indicates that often no improvements are apparent for 3 or 4 days, and then improvement may be very gradual). Temperature, pH, and other factors can all impact treatment efficacy.
A lot of people have sent me questions about their goldfish disease problems. I don't know much, but I'm happy to try to help as time allows. However, before sending me a note asking for help, please read the following.