Names: White Spot Disease, Ick
Disease Type: Parasitic Protozoan/Ectoparasite
Cause/Organism: Ichthyophthirius multifiliis
Ichthyophthirius multifiliis (commonly known as freshwater white spot disease, freshwater Ich or freshwater ick) is a common disease of freshwater fish. It is caused by the protozoan Ichthyopthirius. Ich is one of the most common and persistent diseases in fish. The protozoan is an ectoparasite. White nodules that look like white grains of salt or sugar of up to 1 mm appear on the body, fins and gills. Each white spot is an encysted parasite. It is easily introduced into a fish pond or home aquarium by new fish or equipment which has been moved from one fish-holding unit to another. Once the organism gets into a large fish culture facility, it is difficult to control due to its fast reproductive cycle and its unique life stages. If not controlled, there is a 100% mortality rate of fish. With careful treatment, the disease can be controlled, but the cost is high in terms of lost fish, labor and cost of chemicals.
Whitespot is very damaging to the gills and skin. In heavily infected fish, it can cause a rapid deterioration of condition, considerable distress and death. Infected fish have small white spots on the skin and gills and produce excess mucus due to irritation. Whitespot causes most damage when entering and leaving the tissues of the fish. This can lead to the loss of skin and ulcers. These wounds can harm the ability of a fish to control the movement of water into its body. Damage caused to the gill tissue of an infected fish can also reduce respiratory efficiency. This means it is more difficult for the fish to obtain oxygen from the water, and the fish becomes less tolerant to low levels of dissolved oxygen.
Initially, the fish rub against hard objects trying to dislodge the parasites. As the disease progresses, the fish becomes lethargic, fins are held close to the body, appetite is reduced and the fish loses weight. A key symptom is difficulty breathing, resulting in rapid gilling.
The entire Ich cycle takes approximately two weeks from start to finish. Not all stages of the Ich’s life cycle are susceptible to treatment. Higher temps will shorten the cycle, while low temps lengthen it. Therefore, raising the water temp shortens the time it takes for the parasite to reach the stage in which it is susceptible to medication.
Treatments must be given for a long enough period to assure that all parasites are gone. Watch carefully for other infections as secondary infections often occur where the skin has been damaged by the parasite.
Use treatment as directed on the package instructions; however, cut dosages in half when treating scaleless catfish and tetras. Regardless of the medication used, treatment should be given continuously for 10-14 days to ensure all parasites are killed. Between treatments, a partial water change is recommended. Keep water temperatures higher than usual to speed up the life cycle of the parasite. Discontinue carbon filtration during treatment as it will remove the chemicals.
The best way to avoid Ich is to quarantine all new fish in a separate tank for two weeks before moving them to the regular tank. When quarantine is not possible, a prophylactic treatment (such as Mardel Coppersafe®, FritzPro Methylene Blue or Malachite Green) given when new fish are introduced and again four days later will help reduce the incidence of infection. New plants should also be treated as they can carry Ich cysts.
Maintaining high water quality, avoiding temperature fluctuations and providing a robust diet is the best preventative for Ich and other diseases.