Nerdy Science Blog

Saprolegnia is a fungus that is a normal component of freshwater aquarium environments. It feeds on dead and decaying matter helping to rid the aquarium of waste. When an aquarium is properly maintained, Saprolegnia is harmless to healthy fish. However, when the water of an aquarium becomes overly littered with decaying matter, or when fish become sick or develop wounds, Saprolegnia can harm fish.

Saprolegnia spores are present in most all freshwater aquariums. The spores are not visible and will circulate silently until a suitable substrate is present for its attachment. Saprolegnia spores target dead fish that have not been removed from the tank, uneaten fish food, infertile fish eggs, and wounds that may be present on live fish. Saprolegnia presents as white to gray patches on the skin of fish that become more hair-like, and cottony as the disease progresses. If left untreated, Saprolegnia can erode into deeper tissues of the fish and disrupt internal body fluids leading to death of the fish.

Treatment of Saprolegnia in aquarium fish involves removing infected fish from the tank, placing them in a separate tank or bowl, and adding an agent to the water of this tank to disrupt the growth process of the fungus. Success of treatment depends on the extent of the body of the fish that is covered with the fungus. Some agents that can be added to the treatment tank include, salt, malachite green, potassium permanganate, methylene blue, antifungal medications, and copper. Each agent should be used under certain conditions and directions should be followed carefully to avoid causing further damage to infected fish.

Though there are many treatments that can be effective when Saprolegnia attacks aquarium fish, preventative measures are easy and necessary to ensure aquarium fish remain free of Saprolegnia infections. Preventing Saprolegnia outbreaks in an aquarium begins by maintaining healthy water. Fostering healthy aquarium water includes, small and frequent water changes, removing dead fish, vacuuming excessive decaying food, keeping the pH of the water in certain parameters, maintaining minerals, such as calcium at proper levels, preventing the buildup of ammonia and nitrites in the tank, not overfeeding fish, and adding live plants to the aquarium.

Water change is essential in removing waste products, nitrates, phosphates, ammonia and nitrites and also for replacing trace elements in the tank. Monitoring the levels of ammonia, nitrites, and pH of the water is also very important. High levels of ammonia and extremes of pH can cause burns to fish resulting in wounds to which Saprolegnia can attach and proliferate. High nitrite levels are toxic to fish and should also be monitored.

In addition to maintaining clean, healthy water, monitoring fish for wounds that may be caused by attacks from aggressive fish, sharp surfaces in the tank, or from rough netting and fish handling technique is helpful in prevention. Removing these hazards and handling fish carefully can help prevent wounds that become surfaces for Saprolegnia attachment and infection.

Saprolegnia is a normal part of clean, healthy, freshwater aquariums. Healthy fish are generally safe from infection by Saprolegnia. Clean water, vigilant monitoring, and removal of waste products from the aquarium will promote healthy fish. Prevention is the easiest method for controlling Saprolegnia outbreaks. However, when prevention fails, there are treatments available that can be effective in curing infected fish.

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