Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2019
Publication Date: 3/13/2019
Citation: Straus, D.L., Ledbetter, C.K., Heikes, D.L. 2019. Inhibiting fungus on largemouth bass eggs with copper sulfate and its toxicity to fry and juveniles. Journal of the World Aquaculture Society. p. 1-10. https://doi.org/10.1111/jwas.12631.
Interpretive Summary: Copper sulfate is used for fungus control on eggs in fish hatcheries. In this study, we determined that 40 parts per million copper sulfate, applied daily until hatch, was needed to control fungus on largemouth bass eggs in the very high alkalinity/hardness waters of a local commercial largemouth bass producer. We also determined the toxicity of copper sulfate to largemouth bass fry and juveniles to allow for safe treatments. This study confirms that copper sulfate is an inexpensive, important resource for hatcheries to control egg fungus, especially in waters of high alkalinity/hardness. The cost to treat a hatching tank to control egg fungus using formalin, hydrogen peroxide and copper sulfate were $1.50 USD, $2.86 USD and $0.05 USD, respectively.
Technical Abstract: This study determined the effectiveness of copper sulfate pentahydrate (denoted CuSO4) to inhibit fungal growth (caused by Saprolegnia spp.) on largemouth bass (LMB; Micropterus salmoides) eggs spawned on/in fiber mats in high alkalinity/hardness waters (384 mg/L and 452 mg/L, respectively); experiments also determined toxicity of CuSO4 to LMB fry and juveniles. An untreated control and three CuSO4 concentrations (10, 20, and 40 mg/L) were tested under a flow-through scenario in the effectiveness experiment. Eggs were treated daily until hatching began. Fungal load at time of hatch was heavy in the untreated controls, moderate in the 10 and 20 mg/L treatments and light in the 40 mg/L CuSO4 treatments. Fungus samples were identified as Saprolegnia salmonis through genetic sequencing. The 24 h median lethal concentration (LC50) values on LMB sac and swim-up fry were 32.0 and 4.6 mg/L CuSO4, respectively; the No Observed Effect Concentrations (NOEC) were 16.0 and 0.125 mg/L CuSO4, respectively. Swim-up fry were very sensitive to CuSO4, as would be expected. Juvenile LMB are extremely tolerant to CuSO4 and their 24 h LC50 value was 185.5 mg/L; the NOEC was 64 mg/L. This is our latest study to confirm that CuSO4 is an inexpensive, important resource for hatcheries to control egg fungus, especially in this study with high alkalinity/hardness waters.