Optimizing copper sulfate treatments for fungus control on channel catfish eggs.

This range-finding study determined the optimum concentration of copper sulfate (CuSO4) for fungus control on eggs of channel catfish Ictalurus punctatus. The study consisted of five CuSO4 concentrations (2.5, 5, 10, 20, and 40 mg/L) and an untreated control in a flow-through system. A single spawn was used for each replication (N=4). Eggs were treated daily until the embryos reached the eyed stage. When hatching was complete for all viable eggs, fry were counted to determine the percent survival in each treatment. Fungal growth was severe in the untreated controls; survival of hatched fry in the control group was approximately 2%. The optimum CuSO4 treatment, as determined by percent survival of hatched fry, was 10 mg/L daily (69% survival); survival for this treatment group was significantly different from that for the controls. Very little fungus was present in treatments receiving 10-mg/L CuSO4 or higher except in one replication that had approximately 40% unfertilized eggs. The average survival rates in the 0-, 2.5-, 5-, 10-, 20-, and 40-mg/L CuSO4 treatments were 2, 34, 50, 69, 59, and 51%, respectively.