|JOHNSON, J - Iowa Department Of Natural Resources|
|ESSER, RANDALL - Iowa Department Of Natural Resources|
|Ledbetter, Cynthia - Cindy|
|Straus, David - Dave|
Submitted to: Aquaculture America 2015-Book of Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 1/17/2015
Publication Date: 2/19/2015
Citation: Johnson, J.A., Esser, R., Ledbetter, C.K., Straus, D.L. 2015. Managing Ich infections of walleye cultured in a surface water supply with copper sulfate [abstract]. Aquaculture America 2015-Book of Abstracts. p. 238.
Technical Abstract: Ichthyophthirius multifiliis infests walleye during growout at Rathbun Fish Hatchery (RFH). Daily flow-through formalin treatments (45-50 ppm for 9 h) were applied to prevent Ich outbreaks, and this contributed to 25% ($35,000) of fish production costs during the grow-out period. Research to decrease formalin application began in 2006 and has made gradual progress in reducing formalin use. Recent studies have evaluated copper sulfate (CuSO4) as an alternative to formalin to reduce the cost of controlling Ich infections in walleye. A range-finding trial was conducted to determine the maximum safe dosage (no mortality) for CuSO4. Test containers were treated with 0.15 to 4.8 mg/L CuSO4 and aerated for 48 hours with no water exchange; no mortality was observed at concentrations of 0.15, 0.3, 0.6, and 1.2 mg/L after 48 h. A second trial compared Ich infection rates and growth rate of walleye given a 2-L purified water treatment (control) or the therapeutic rate (alkalinity/100) of CuSO4 dissolved in 2 L of purified water. An Ich outbreak was established in twelve tanks that contained walleye fingerlings by maintaining a 2.0-h exchange rate as compared to the typical 0.5 to 1-h exchanges in research tanks. Treatments began once the infection rate reached 15 Ich cells/gill arch in one tank and nine consecutive daily treatments were given. Fish in tanks treated with CuSO4 had significantly lower (P<0.05) Ich infection rates (6.6 cells/arch) than fish in control tanks (395.8 Ich cells/arch) at the end of the post-treatment period. Growth of fish in control tanks was significantly higher (P<0.05) at 1.6 mm/d compared to a growth rate of 1.2 mm/d for fish in tanks given the CuSO4 treatment. The third trial compared growth rates of walleye treated at the therapeutic rate and untreated in 200 L fiberglass tanks with flow-through well water (no Ich). There were 94 fish/tank; fish averaged 9.2 cm and 6.2 g. The CuSO4-treated tanks received daily treatments for 5 d and were untreated for 14 d, this was repeated; the study lasted for 50 d (n=3). Fish in untreated tanks averaged 14.5 cm and 25.2 g and fish in CuSO4-treated tanks averaged 14.6 cm and 25.3 g. Growth rate was 1.1 mm/d for all tanks. Copper sulfate treatments did not cause fish mortality and controlled Ich infections, but resulted in reduced growth rates in one trial.