Rotenone has little effect on water quality, phytoplankton, zooplankton or macroinvertebrates in aquaculture nursery ponds

Authors: MISCHKE, CHARLES - Mississippi State University; Richardson, Brad; WISE, DAVID - Mississippi State University; TIWARI, AMBIKA - Mississippi State University

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2022
Publication Date: 1/9/2023
Citation: Mischke, C.C., Richardson, B.M., Wise, D.J., Tiwari, A. 2023. Rotenone has little effect on water quality, phytoplankton, zooplankton or macroinvertebrates in aquaculture nursery ponds. North American Journal of Aquaculture. https://doi.org/10.1002/naaq.10276.
DOI: https://doi.org/10.1002/naaq.10276

Interpretive Summary: Rotenone is a natural toxicant derived from tropical plant roots. In aquaculture, rotenone is typically used to remove unwanted fish in stocked ponds or prior to stocking fry or fingerlings. Unfortunately, rotenone has been reported to cause significant declines in zooplankton and macroinvertebrates, taking months to recover. To determine whether rotenone has long-lasting impacts on aquaculture ponds, scientists at the USDA, ARS, Warmwater Aquaculture Research Unit and Mississippi State University exposed 9 experimental ponds to one of 3 treatments including untreated control ponds, rotenone application, and rotenone application followed by potassium permanganate neutralization. Results showed that zooplankton populations recovered within 2 weeks in all treatments and there were no noticeable impacts on predatory macroinvertebrate species. This study suggests the use of rotenone would not significantly alter typical catfish stocking regimes, but did not provide any control over predatory macroinvertebrates thus this source of potential loss should be mitigated by other strategies.

Technical Abstract: Rotenone application has been reported to cause significant declines in zooplankton populations with cladocerans and copepods being the most susceptible and possibly taking months to recover. Because copepods and cladocerans are preferred by catfish fry, rotenone application could have significant effects on nursery pond production. Effects of rotenone on zooplankton and time required for recovery has not been studied in eutrophic aquaculture ponds that are typically drained and refilled yearly. We quantified the effects of rotenone application to either mostly drained ponds or full ponds on water quality, phytoplankton, zooplankton, and aquatic macroinvertebrates in experimental ponds. For the drained pond study, 9 ponds were drained to about 15 cm water. Six ponds were treated with 4 µL/L rotenone; three of the treated ponds were then treated with 4 mg/L potassium permanganate (KMnO4). The three additional ponds were drained but untreated. All ponds were then filled and fertilized. In the full pond study, 9 full ponds were treated with 4 µL/L rotenone. Three of those ponds were then treated the next day with 4 mg/L KMnO4. Three ponds were left as untreated controls. For established catfish aquaculture ponds in the southeastern United States, applying rotenone to ponds with 15 cm or less water has no effect on water quality, phytoplankton, or zooplankton. Neutralization with KMnO4 did not affect any measured variables. Fry could be stocked 11-14 d after treatment if the pond is fertilized. If a whole pond is treated with rotenone, no effects on catfish fry production should occur. Ponds could be stocked about 7 d after treatment if neutralized with KMnO4 and about 11 d after treatment without neutralization. However, rotenone treatment did not reduce predatory macroinvertebrate risk, and this should be addressed using additional management strategies.