More correctly, we will discuss white spots on marine tropical fish. There are actually several white spot illnesses which marine tropical fish can get. Correctly and promptly diagnosing which your fish has is the first step to successfully treating your fish.
The earliest symptoms of Cryptocaryon are fish scraping on coral and
decorations. As the parasite progresses white spots or pimples about the size of a
pinhead will appear on the fish's body and color may fade. In advanced cases the
fish will appear as if it has been sprinkled with salt, breathe heavily and scrape
frequently. The earlier the infestation is recognized the more successful treatment
is likely to be. Cryptocaryon is often confused with Lymphocystis.
When whole aquariums of fish are lost in a short period of time it is usually to oodinum. Oodinum is a parasite which first attacks the gills. Therefore, heavy breathing is the earliest recognizable symptom. As the infestation advances, the body will take on a powdery or velvet-like appearance. The spots are much smaller than Cryptocaryon spots. Oodinum can kill fish in less than a week! Careful observation of your fishes' respiration rate is important for an early diagnosis. By the time your fish has a velvety appearance, it may be too late!
Lymphocystis is frequently mistaken for Cryptocaryon or ich. However, Lymphocystis is a virus rather than a parasite. Lymphocystis frequently appears on the edges of fins and occasionally on the body as cauliflower- or cotton-like nodules. The nodules are considerably larger that Cryptocaryon or oodinum, usually 1/8 inch in diameter or larger. Except in extreme cases, the nodules usually do not number more than 6-10. Frequently there may be only 1 or 2. The lymphocystis nodules rarely multiply nor do they enlarge markedly.
The treatment of choice for Cryptocaryon is an ionic copper compound such as Copper Tru. Copper concentrations should be tested daily and kept in the .15 to .20 ppm range for a minimum of 14 days. In severe cases, a freshwater dip for 3 to 5 minutes in dechlorinated tap water the same temperature and pH as the aquarium may be warranted. Other treatments such as dye medications (RidIch+ or Marin Oomed), medicated food (Tetra parasitic) or chelated copper (Coppersafe) have also proven successful and can be used in many situations.
The treatment of choice for oodinum is an ionic copper compound at the same concentration and duration as above. Also, in severe cases a freshwater dip is an option. Chelated copper compounds can also be effective. Medicated foods and dye medications are often ineffective against this fast acting parasite. The oodinium spores can survive in the aquarium without a host for up to 4 weeks! Frequently a reinfestation can result from the hobbyist's rush to replace recently lost fish.
Both Cryptocaryon irritans and Amyloodinium ocellatum go through a multi-stage life cycle. The lesions seen on the fish are one stage. However, the medications do not affect the parasite in this stage. The medications only affect the free swimming stage of the parasite. For this reason, it is especially important to carry through with the full term of treatment and to not add fish to the tank while treating.
Treatment for lymphocystis is quite simple. Left alone the nodules will eventually fall off. This may take a month or longer. Since lymphocystis is neither contagious nor destructive this is the preferred treatment. Some books suggest removing the nodules. This is extremely stressful on the fish and the possibility of reinfection is high. The best treatment is to watch the fish closely and let the virus run its course.
We have described the symptoms and treatment of the three most common white spot illnesses of marine tropical fish. Along with treatment, the hobbyist must look at the underlying cause of the infestation.
Cryptocaryon and oodinium are opportunistic parasites that take advantage of the fishes' reduced resistance due to stress. Many things place stress on your fish. A recent transfer from store to home or from tank to tank at home, poor diet, poor water quality, overcrowding, being chased by aggresive tank mates, and fighting are just some of the factors which stress your fish. In addition to treating as indicated above, a full range of water tests should be performed. If indicated, partial water changes should be done. Water changes may also be done after treatment to reduce medication levels in your tank.
A World Of Fish has many experienced marine aquarists on staff to assist you in identifying your fishes' illness. We can also recommend a course of treatment.
Suggested reading: Marine Fish, The recognition and treatment of diseases; Robert R Clifton.
Aquariology - Master Volume - The Science of Fish Health Management; Tetra Press.