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.
Two dose confirmation studies are required by the U.S. Food and Drug Administration to verify the effectiveness of a candidate before approval as a new animal drug is awarded; the two studies provide independent substantiation of the results. This laboratory study was designed to compare an untreated control and a 10-mg/L copper sulfate (CuSO 4 ) treatment to control fungus (Saprolegnia spp.) on eggs of channel catfish Ictalurus punctatus at 23.58C in a flow-through system. The eggs were treated once daily until the embryos reached the eyed stage (five treatments). When hatching was complete for all viable eggs (day 10), the fry were counted to determine the percent survival in each treatment. Infestation by a fungus identified morphologically and by polymerase chain reaction as Saprolegnia spp. was severe in the control fish, resulting in 8% survival. The mean percent survival of fry hatched from the CuSO 4 -treated eggs was significantly higher (mean, 55%; range, 27-71%).
Cat¢sh hatcheries use copper sulphate pentahydrate (CuSO 4 Á 5H 2 O) as an economical control for saprolegniasis on eggs. This study determines hatch rate of channel cat¢sh, Ictalurus punctatus (Ra¢nesque 1818), eggs in hatching troughs containing 23.8 1C £ow-through well water when treated with 100 mg L À 1 CuSO 4 Á 5H 2 O (10 times the proposed therapeutic dose). Eggs were treated daily until the embryos reached the eyed stage. Fry survival in the control and 100 mg L À 1 CuSO 4 Á 5H 2 O treatments was signi¢cantly di¡erent (15% and 71% respectively). This study demonstrates that there is a considerable margin of safety in using CuSO 4 Á 5H 2 O as a cat¢sh egg treatment to control saprolegniasis.
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