Fungus on fish eggs isn’t just an eyesore for the aquaculture industry; it’s also deadly to fish and expensive to treat. U.S. Department of Agriculture scientists have found that copper sulfate kills fish egg fungus and is cheaper than current treatments.

Scientists with USDA's Agricultural Research Service (ARS) previously compared the effectiveness of copper sulfate to treat catfish eggs against two current treatments: formalin and hydrogen peroxide. While both are approved for use by the U.S. Food & Drug Administration, they are more expensive than copper sulfate. Hydrogen peroxide costs 89 cents per treatment, formalin costs 73 cents and copper sulfate costs 2 cents.

To learn if copper sulfate was effective treating other types of fish eggs, fish toxicologist David Straus at the ARS Harry K. Dupree Stuttgart National Aquaculture Research Center in Stuttgart, Ark., treated the eggs of sunshine (hybrid striped) bass with copper sulfate. Straus and his team worked with hatchery managers of Keo Fish Farm, the largest producer of sunshine bass fry and fingerlings (young fish) in the world. They found that eggs treated with copper sulfate had a nearly 50% survival rate. Untreated eggs survived 28% of the time.

Copper sulfate proved a cheap and effective way of controlling fungus with sunshine bass eggs. Toxicity experiments on sunshine bass larvae also showed that copper sulfate is a safe and valuable resource for controlling fungus in hatcheries.

Scientists are working toward gaining FDA approval to use copper sulfate on catfish eggs to treat fungus as well as Ich, a parasite that infects the gills or skin of fish and eventually kills them.