Use of copper sulfate to control Saprolegniasis at a commercial sunshine bass hatchery

Authors: Straus, David - Dave; Farmer, Bradley; Ledbetter, Cynthia - Cindy; Beck, Benjamin; WILLIAMS, RICK - Keo Fish Farm; CLARK, MIKE - Keo Fish Farm; FREEZE, MIKE - Keo Fish Farm

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2016
Publication Date: 6/15/2016
Citation: Straus, D.L., Farmer, B.D., Ledbetter, C.K., Beck, B.H., Williams, R.S., Clark, M.L., Freeze, M.T. 2016. Use of copper sulfate to control Saprolegniasis at a commercial sunshine bass hatchery. North American Journal of Aquaculture. 78:243-250.

Interpretive Summary: Copper sulfate is routinely used in the catfish industry by hatchery managers to prevent fungus from growing on eggs while they are incubated in hatching troughs with flow-through well water. We wanted to know if it would be effective in hatcheries with different types of hatching systems. This study was designed to see if copper sulfate would be effective to control fungus on sunshine bass eggs hatched under constant flow in a McDonald type jar; these containers have water from the supply hose directed down to the bottom-center of the jar to provide a constant upwelling motion lifting the eggs in a gentle swirl. We found that it was very effective at the rate of 20 parts per million copper sulfate for a 10 minute bath. This rate is very low and copper is flushed out of the hatching containers within a few minutes. We also determined the amount of copper sulfate that would be safe for 2 day old larvae. Research like this is important information that is needed by the aquaculture industry to fight fungus problems on eggs.

Technical Abstract: An obstacle to sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) larval production is fungal growth on eggs caused by the water-mold Saprolegnia spp. Copper sulfate (CuSO4) is commonly used for fungus control in troughs of catfish hatcheries, but the effectiveness on other fish egg hatching systems was unknown. Because sunshine bass eggs begin hatching after 48 h, CuSO4 treatments (0, 10, 20, and 40 mg/L) began immediately the afternoon of spawning with a 10 min aerated, static bath and was repeated the morning and afternoon of Day 2; eggs were not treated after hatching began. An in vitro assay was developed for this treatment regimen that indicated maximum fungal inhibition was achieved with 20 mg/L CuSO4. For the effectiveness experiment in hatching jars (n=3), fungus was severe in the untreated controls (27.7 % survival), but very little fungus was present in treatments receiving 10 mg/L CuSO4 (31.4 % survival) or higher. The highest survival was at 40 mg/L CuSO4 (50.5 % survival); however, the 20 mg/L CuSO4 treatment (45.8 % survival) was not significantly different from the 40 mg/L treatment and allows for a greater margin of safety. Fungus samples were identified as Saprolegnia ferax through genetic sequencing. Toxicity experiments on sunshine bass larvae indicated the 24 and 48 hLC50 values were 5.4 and 3.91 mg/L CuSO4, respectively; the No Observed Effect Concentrations (NOEC) were 0.5 and 0.25 mg/L CuSO4, respectively. This study confirms that CuSO4 can be an economical and valuable resource in hatchery management for control of saprolegniasis in McDonald jars.