Catfish are a resilient and abundant species of fish that flourish in both salt and fresh water. Known as "bottom feeders," catfish generally prefer muddy or brackish water and scavenge the bottom of the waters for food. Catfish grown in cultured ponds, hatcheries and aquariums sometimes show symptoms of disease in the form of fungus. The fungus can ruin an entire stock of catfish or taint an aquarium if proper water quality is not maintained or controlled.
Winter Saprolegniasis, commonly referred to as winter fungus, is the most commonly occurring fungal infection in cultured channel catfish. This disease is also referred to as winter kill syndrome and is caused by the fungal family of Saprolegniaceae. Winter kill syndrome, however, is a term that is sometimes used to describe the death of fish in ice covered waters but is not related to the fungus. In winter fungus particularly, the specific species of Saprolegnia that causes this disease has yet to be identified, and the cause for the disease is largely attributed to change in water temperature and stress from crowding. Winter fungus normally occurs during the months of October and March, or when water temperatures dive below 59 degrees Fahrenheit. The appearance of winter fungus is noticeable by brown cotton-like patches of growth on the skin and gills, sunken eyes and skin with altered or bizarre pigmentation.
A member of the Saprolegniaceae fungus family, Branchiomyces is the culprit that causes Branchiomycosis. This is a relatively new fungal disease in cultured catfish and typically affects only smaller catfish fingerlings and fry. The disease has only been reported in nursery ponds with a water temperature exceeding 68 degrees Fahrenheit. The disease typically affects fish that are no more than two months old, and as of 2010, no known treatment or preventative measures have been implemented. The fungus is only visible through a microscope, and the disease directly targets the intravascular blood vessels of the gills and gill arches. Fungus will form in the gill region, swell and block oxygen, directly affecting respiration and ultimately causing death.
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Simple measures for preventing winter fungus are usually implemented throughout the year, typically by maintaining proper water quality and reducing the crowding of overstocked catfish ponds. Maintaining the proper level of chloride present in the water is essential to proper water quality, and it also deters nitrite toxicity. Measures are normally taken to prevent winter fungus in late summer and fall by reducing the population of the stock, harvesting and selling the fish before the winter season. The act of reducing the stock is believed to reduce the stress in a crowded pond environment. Pond depth is also attributed to helping maintain a disease free environment. Deeper ponds can allow fish to acclimatize to water temperature changes easier, so pond depth should be kept at maximum levels.
Experimental Strategies for Treatment
Prevention and treatment strategies are still being researched and investigated to combat Saprolegniaceae. Certain methods that have been studied involve using prophylactic chemical agents to minimize the amount of pathogenic zoospores present in a pond. The use of adjusted amounts of formalin, copper sulfate and diquat have shown in some laboratory experiments to prevent development of Saprolegnia infections, as these agents effectively reduce fungal zoospores. Other methods to be considered for future use in controlling Saprolegnia include the use of certain fungicides. Hydrogen Peroxide and Bronopol have already been approved by the FDA for use on fish eggs as an anti-fungal treatment, and they may be considered for treatment of fungus on larger fish populations.
Cotton Wool Disease
Cotton wool disease is more common in large aquariums and is easily noticeable by the cotton-like spores that form around the gills and mouth of the catfish. The term Cotton wool disease is also a general term used to describe many types of fungus with a cotton-like appearance. Achyla, a member of the Saprolegniaceae family, is largely responsible for this fungal disease. Salt baths are the most common treatment for this problem, as well as applying antifungal agents such as phenoxyethanol. Many times, the tank is emptied and cleaned of organic waste matter collecting at the bottom of the tank. Accumulation of organic waste, crowded tanks and poor overall water quality are thought to cause this fungus to form in most aquariums.