Pine Bluff, AR — Mid to late winter is a quiet time for ponds in Arkansas. Low temperatures keep warmwater fish species lethargic and feeding less often. Something else that slows down during winter are fish immune defenses, leaving them at higher risk of infection and mortality, Scott Jones, small impoundment Extension specialist at the University of Arkansas at Pine Bluff, said.
“A common winter disease known as saprolegniasis, or ‘winter fungus,’ can hit catfish particularly hard,” Jones said. “Saprolegniasis is a fungal infection that presents as pale grey to white fuzzy cotton-like textures on the skin and scales of fish. The infection can spread to muscle and tissue beneath the skin. The appearance is similar to fungal growth on old fruit beginning to spoil. Associated abnormalities include sunken eyes, discolored skin and aimless wandering near the waters surface.”
While some recover, the mortality for infected fish is usually high. Older and weaker fish are at higher risk. It is common to lose a few fish of various species each winter to saprolegnia, he said. Further investigation is encouraged when dozens to hundreds of fish are found dead or infected; this may indicate a water chemistry problem.
“Ponds in Arkansas that experience severe or chronic outbreaks of saprolegnia often have low pH, alkalinity and/or hardness levels. This condition impacts fish fitness more than the abundance or efficacy of the fungi,” Jones said. “Warmwater fish immune defenses are naturally slower and weaker to respond to pathogens during cold months. Sub-optimal water quality makes it more difficult for fish to maintain ideal blood chemistry. The combined effects can reduce immune response further, allowing disease to develop in otherwise healthy fish.”
There are no practical whole-pond treatments that can stop saprolegnia infections. Some chemical treatments have been used in the aquaculture industry to combat saprolegnia, but few work well and those that do often come with hazards to the fish, applicators or the environment, he said. Short-term high dose emersion treatments can help reduce fungal infections, but they require affected fish to be captured, handled, treated and returned to the pond which is itself a laborious and stress-inducing action.
“The most practical approach for pond owners to prevent large-scale saprolegnia outbreaks is to maintain good water quality, to not over-stock and to manage the fishery so that all species are in good condition, plump and healthy,” Jones said.
University of Arkansas at Pine Bluff fisheries specialists can help diagnose and prescribe solutions to disease outbreaks for both commercial fish producers and private waters. Commercial fish producers are encouraged to contact the Fish Health and Disease Diagnostic Laboratory in Lonoke for diagnostics.
For assistance, contact Dr. Grace Ramena, director of fish health/diagnostics at the Pine Bluff and Lonoke labs, at [email protected] or (870) 575-8137. Kailash Bohara, Extension specialist, is headquartered in Lonoke and can be contacted at [email protected] or (501) 676-3124. Scott Jones, Extension specialist headquartered at UAPB, can be contacted at [email protected] or (870) 575-8185.
