Rotenone has been used for centuries by fishermen to harvest fish. More recently, scientists and fishery managers have used rotenone to sample fishes and remove unwanted species from freshwater systems. But how does this toxic chemical work so effectively to kill fish, is it toxic to other species including humans, and are the benefits of using this chemical worth the risks? Find out below.
|A 3-D image of the chemical structure of rotenone. http://en.wikipedia.org/wiki/Rotenone|
Rotenone is a naturally occurring chemical found in the roots, seeds, and leaves of several subtropical plants and has been commonly used as a piscicide or fish killer. This piscicide is non-selective, meaning it has the potential to kill any fish exposed to it. However, as with any chemical, the dose and duration of exposure determine how toxic it is.
|The Yam Bean plant is a natural source of the organic poison rotenone. Source http://treefrogpermaculture.com.au/?p=290|
|Fish kill using rotenone. http://www.encyclopedia.com/doc/1E1-X-rotenone.html|
Indigenous fishers have traditionally crushed native rotenone-containing-plants and applied them to marine and freshwater to catch fish. Fishery managers often use large quantities of rotenone to kill-off invasive or unwanted fishes in freshwater systems, then restock the system with native fish to conserve the natural ecosystem or to support recreational fisheries. Scientists have also used rotenone as a tool to assess fish diversity and abundance in marine and freshwater environments.
|Fishermen smash barbasco roots with a piece of wood, then dip and shake the smashed roots in the water, releasing rotenone. Poisoned fish come to the surface, easy to take with a net. Source: http://amazon-explorer.blogspot.com/2012_08_01_archive.html|
Rotenone has several characteristics that make it desirable as a tool to sample fish and eradicate invasive fish species. Chief among these characteristics are that it degrades quickly in the environment and from fish tissue (often on the order of days), it does not bioaccumulate, and it is not as toxic to birds, mammals or aquatic insects as it is to fish. To lessen the impacts of rotenone treatment on non-target species scientist often suggest using the lowest rotenone concentration and duration needed to remove the target species.
|New York Department of Environmental Conservation apply rotenone to a pond to kill non-native fish and restore the system to the historic natural community. Source: http://www.dec.ny.gov/outdoor/31920.html|
In marine systems, the benefits of sampling with rotenone are widespread. For instance, we owe much of our current knowledge and identification guides of marine shore fishes to rotenone. This is particularly true for cryptic species and those fishes that live in turbid and deep-water environments where visual surveys are less successful. Rotenone is also a very useful tool in assessing fish biodiversity and population densities near shore. Many other collection techniques for marine shore fishes are more selective and destructive to habitat in comparison (e.g. traps and nets).
|A pile of Asian carp and other fish killed with rotenone. Source: http://whyfiles.org/2012/putting-the-brakes-on-fish-invasions/|
The main human health hazard associated with rotenone usage in fisheries management (and research) arises from inhalation of powder or spray, which can be prevented through the use of respirators. There are no reported effects on human consumers of fish collected using rotenone and because rotenone is degraded at higher temperatures, cooking would further degrade any of the rotenone left in the fillet.
|Visual survey of reef life. Rotenone can be used in small sampling areas with visual surveys to get a more complete picture of fish diversity. Source: divingnelsonbay.weebly.com|
However, there has been some controversy over the use of rotenone in aquatic systems based on several studies linking rotenone to Parkinson’s disease. The root of this controversy lies with a study published in 2000. In that study, rats exposed to continuous intravenous rotenone displayed degenerative neurological symptoms nearly identical to Parkinson’s disease. The American Fisheries Society assessed the study and noted it has little relevance to rotenone usage in fisheries management.
|Coral reefs provide habitat for thousands of marine species. Source: http://sanibelseaschool.org/classroom/coral-reefs-in-the-gulf-of-mexico|
The American Fisheries Society also maintains that rotenone is generally not absorbed by the mammalian digestive system, that no Parkinson’s-like symptoms or anatomical changes were produced in rats that were fed rotenone over extended periods in previous studies, and there is no evidence of any link between use of rotenone in fisheries management over many decades and Parkinson’s disease in humans.
Although, as a reaction to the studies linking rotenone to effects on humans, rotenone use has been banned in many marine systems and has come into question in freshwater systems as well.
Tell us what you think. Should fisheries scientist and managers be allowed to use rotenone to remove invasive species and assess biodiversity in marine nearshore habitats? Another question not addressed here but often discussed, do fisheries scientists resort to rotenone use too frequently to eradicate an unwanted species when other methods could be applied?
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