Title: The safety and effectiveness of CuSO4 to control fungus on egg masses in catfish hatcheries Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 24, 2013
Publication Date: February 11, 2013
Citation: Straus, D.L., Mitchell, A.J., Farmer, B.D., Ledbetter, C.K., Carter, R.R., Steeby, J.A. 2013. The safety and effectiveness of CuSO4 to control fungus on egg masses in catfish hatcheries [abstract]. 2013 Mid-Continent Warm Water Fish Culture Workshop, February 4-6, 2013, Mt. Magazine State Park, Paris, Arkansas. p.29. Technical Abstract: Copper sulfate (CuSO4) is widely used by the catfish industry as an economical treatment to control fungus (Saprolegnia spp.) on channel catfish eggs. This is an overview of our effectiveness and safety studies for the proposed indication ‘to control egg mortality associated with Saprolegniasis infecting channel catfish eggs’. Channel catfish were spawned on-site and spawns were moved to the hatching lab within 24 - 48 hrs. Similar portions of a single spawn were placed into mesh baskets of individual compartments of a customized hatching trough and acclimated for 1 hr in 23.5 deg C well water. Egg counts on smaller samples were also determined for each spawn to estimate number of eggs in each compartment. The Effectiveness range-finding study consisted of 5 CuSO4 concentrations (2.5, 5, 10, 20, and 40 ppm) and an untreated control. Eggs were treated daily until the embryos developed eyes. Chemistry of the well water was pH 7.5, 220 ppm alkalinity, and 90 ppm hardness. When hatching was complete for all viable eggs, fry were siphoned into individual jars containing 70% ethanol and counted within a few days to determine the percent of fry that hatched in each treatment. Fungus was severe in the untreated controls (2% survival) and the most effective treatment of 10 ppm CuSO4 controlled fungus (63% survival). Very little fungus was present in treatments receiving 10 ppm CuSO4 or higher except in 1 replication (1 spawn) that had numerous unfertilized eggs. Two dose-confirmation studies have been completed to verify the optimum dose of 10 ppm both in the lab and at a commercial hatchery. The Target Animal Safety study was designed to access the safety of CuSO4 to channel catfish eggs when treated at the therapeutic rate (10 ppm) determined above, and also at 30 and 50 ppm CuSO4. Channel catfish were obtained as described above and eggs were treated daily until the embryos developed eyes; exchange rate of the 26 deg C water was 90 minutes (3X the normal rate) during treatments. When hatching was complete, the percent hatch in each treatment was determined. Some fungus developed in the controls at this temperature and mean percent hatch was 40.8%. The percent hatch of the 10, 30, and 50 ppm CuSO4 was 80.1, 64.2 and 80.2%, respectively. The difference between the 10 and 30 ppm CuSO4 treatments was statistically significant, while the difference was not significant between the 10 and 50 ppm CuSO4 treatments. The lower hatch-rate of the 30 ppm treatment is attributed to the random sampling within the original egg masses and the range of hatching rates that are common in the industry. A separate experiment looked at the hatching success when eggs were treated daily until the embryos developed eyes with 100 ppm CuSO4. The water temperature was 24 deg C and the exchange rate during the treatment was 30 minutes. The individual percent hatch of each replication was 62.7, 94.9, 59.7 and 64.8%.