Hatchery managers working with eggs are constantly on guard for fungal growth triggered by water mould, and a recent study looking at fungus control in hybrid striped bass eggs using a copper sulfate (CuSO4) solution has seen considerable success.
Researchers at the US Department of Agriculture, Agricultural Research Service (USDA-ARS) used CuSO4 to stem fungal growth on the eggs of sunshine bass (female White Bass/male Striped Bass) during larval production at the private Keo Fish Farm in Keo, Arkansas.
Under the leadership of Aquatic Toxicologist Dave Straus of the Harry K. Dupree – Stuttgart National Aquaculture Research Center, researchers began CuSO4 treatments (0, 10, 20, and 40 mg/L) the afternoon of spawning with a 10-minute, aerated, static bath that was repeated the morning and afternoon of day 2; eggs were not treated after hatching began (~48 hours). They found 20 mg/L was the optimum dose.
Straus said the UDSDA-ARS, the US Fish and Wildlife Service, and the US Geological Service were tasked back in the 1990's with gaining FDA-approval on more drugs used in freshwater aquaculture, including national fish hatcheries. The research on CuSO4 fell to his Center and this study, as well as the previous research on fungus infesting channel catfish eggs, came out of the program.
The use of CuSO4 is approved by the EPA for use in aquaculture as an algaecide and molluscicide. But it is not approved by the FDA as a drug in aquaculture; however, regulatory action has been deferred while the researchers are working toward gaining this approval. Therefore, its use as a drug is currently acceptable, according to Straus.
"We are trying to gain FDA-approval to treat channel catfish eggs with copper sulfate for fungus control (and controlling Ich in channel catfish ponds)," Straus told Hatchery International.
"When we gain this approval, copper sulfate will be available OTC so a veterinarian will be able to prescribe it for extra-label use for other species. Therefore, we want to give the vets a little information on which to base these prescriptions. Besides channel catfish and sunshine bass eggs, we have studied it on largemouth bass eggs (they spawn on a mat) and rainbow trout eggs (this should be adequate information for salmon eggs as well)."
When asked about any surprises in the study, Straus replied, “Yes, we didn't know copper would be absorbed by or attached to the eggs. They actually turned blue in the higher doses; this shows that copper is taken up by the egg and might give an extended effect. Experiments are underway to examine this.”
— Erich Luening