Aquatic Invasive Species

The northern snakehead (Channa argus) is a delicacy in its Asian homeland.  In the United States however, it is a highly feared invasive species whose spread has not been successfully slowed.  When the snakehead first emerged as an ecological threat in 2002, media reports first described the fish as being capable of surviving weeks out of water and walking miles from one body of water to the next.  In reality, the snakehead’s unusual physiology allows it to survive approximately one day on dry land, possibly up to four in moist muddy areas.  Furthermore, it is the more mundane aspects of this species’ life history, and not the biological rarity of being able to breathe both underwater and on land, that make it such a nuisance species. 

Snakehead are efficient carnivores whose group hunting tactics can rapidly deplete native fish populations.  However, more important to their spread throughout the United states is their ability to tolerate a wide range of water temperatures.  This general diet and wide thermal tolerance have led some experts to estimate that the northern snakehead could invade all of the lower 48 states.

Current efforts at controlling snakehead populations focus on the use of piscicides (poisons designed to eradicate fish) to wipe out the invasive species.  The current piscicide of choice is the toxin rotenone, which is derived from the jicama plant.  Rotenone is 100% lethal to the northern snakehead; however it also kills all other fish in the target area and is rather expensive.   This combination of collateral environmental damage and high cost is what led Duke University research Evan Schwartz to try and develop alternative piscicides for use in slowing the spread of the northern snakehead.

Schwartz and his team of researchers are looking at three new toxins obtained from other plants with known poisonous properties (Nerium oleander, Canabium sativum, and Strychros nux vomica) to determine if a cheaper, and greener, piscicide can be produced.  Their research will include expansive field testing that compares the efficacy of these newly derived poisons to that of rotenone as well as other control techniques such as electro-shocking and netting.  Schwartz says that his research should pose little threat to surrounding populations because rotenone decomposes in sunlight and is also inherently less toxic to humans and other mammals.

From these field experiments, Schwartz hopes to assemble data on how each of the new plant-based toxins compares to rotenone in terms of both snakehead mortality as well as the effect on the native fish populations.  Ideally, one of the tested poisons would retain the same high lethality towards the snakehead as rotenone, but would cause much less collateral damage to the native species.  Yet, this is unlikely and so a more realistic outcome would be to find a plant based poison with both positive and negative effects similar to rotenone that can be more cheaply produced.  This would allow for the broader implementation of snakehead control policies throughout the contiguous United States, hopefully leading to a halt of the spread of this aquatic invader.

Ben Berg

The ongoing fight against invasive species has bred several unique strategies for eradicating the harmful foreign species that now inhabit many ecosystems worldwide. In the case of aquatic species, one such strategy has been the use of the piscicide rotenone, a poison that when dumped into rivers, streams, and lakes kills most living organisms within a given radius.

Besides the ecological concerns associated with the use of such a poison, rotenone is both expensive and in increasingly short supply. An extract of the jicama plant, rotenone has recently been synthesized in a laboratory setting, creating a cheaper and more effective version of the poison, which has higher solubility in water in its synthesized form than its naturally occurring state.

A proposed study by researcher Alex Groszewski, however, highlights the issues associated with the development of synthetic rotenone, and aims to solve these problems through the use of new and different chemicals. “Cheaper and more deadly forms of rotenone only amplify the problems that exist with naturally occurring rotenone.” Groszewski said, commenting on the increased number of native species that will be affected by the more available and effective synthetic rotenone.

Building on existing research by Ashraf et al., Groszewski hopes to uncover chemicals that are equally accessible, yet better than rotenone in their ability to specifically target undesirable species in a given area. No scientific investigation has provided a comprehensive look at such chemicals or their ability to affect certain species more than others. The answers to these questions will thus be important goals of the proposed research.

Groszewski plans to test the effects of extracts of three herbs, Nerium Oleander, Cannabium Sativum, and Datura Alba, which are informally recognized as piscicides by “ artisanal fishermen” surveyed in the Ashraf et al. study. The effects of these extracts will be tested on the Northern snakehead (Chana Argus), sea lamprey (Pertomyzon Marizon), and ruffe (gymnocephalus cernuus).

When asked about the choice of fish to be tested in the study, Groszewski responded, “These are three invasive species that currently threaten the Laurentian Great Lakes region. This is an area species invasion risk is a large concern and because of this they made logical choices as test subjects.” The plan is to dose these potential invaders with the extracts of the above plants as well as synthetic rotenone, and gather data that will allow a comparison of the effects of the respective chemicals. Aquatic species native to the Laurentian Great Lakes region will also be tested to try and find a chemical that is better at targeting invaders than the native ecosystem.

Groszewski is hopeful that his study could prevent the further use of destructive poisons in the elimination of invasive aquatic species. If a more target-specific poison is found, it could prevent some of the damage done by rotenone, which has left some native species’ populations reduced by as much as 21% after a period of five years. He also hopes to find a chemical that could act as a cheaper substitute to the naturally occurring rotenone and that would thus be feasible for large-scale use.

Such a poison would represent a huge leap forward for scientists who have otherwise resorted to using the harmful rotenone or other strategies such as electrified barriers whose effectiveness remains in question. Groszewski’s objectives appear simple yet important to the preservation of aquatic ecology, a combination that makes for compelling possible outcomes. All that remains to be seen is whether or not such a piscicide exists, and if it will be efficient enough to end the use of rotenone in invasive species control.

The northern snakehead has become a widespread invader in the United States. Due to this species’ ability to survive and thrive in many different environments, control efforts for this species must implemented. Poison is one of the various methods being explored. In laboratory testing, several different concentrations proved lethal to the snakehead . Lazur et. al determined that the smallest lethal dose was 0.075mg/L of rotenone, a commonly used aquatic poison. Such a dose killed all test subjects within 1 hour of administration, and proved incredibly effective in a pond setting in Crofton, MD as 8 adult and 834 juvenile snakeheads were recovered. These results demonstrate a susceptibility of this species to known control methods. However, all other aquatic fauna in the affected region succumbed to the poison as well. Additionally, the affected area remained toxic for at least one week after treatment. It is suggested that this method only be utilized in clearly defined and isolated areas.

(North American Journal of Fisheries Management 2006; 26: 628-630)

Expansion of a Northern Snakehead Population in the Potomac River System

Transactions of the American Fisheries Society 136:1633–1639, 2007 doi: 10.1577/T07-025.1

Northern snakeheads (Channa argus) are illegal to posses in the states of Maryland and Virginia. After finding several of these fish in a Maryland pond in 2004, both states created an initiative in order to quantify and eliminate the snakehead “threat.” By way of electrofishing (a system of creating an electrical blast radius in a water body) and traditional hook and reel fishing, a large number of snakeheads were accounted for. The amount of snakeheads caught increased between the years of 2004 and 2006, either by way of informed anglers, or increased breeding.The study came to several conclusions. The majority (>80%) of the fish caught originated from a single point, showing a central nest location. They then began to migrate downstream in an attempt to find more food and nesting grounds. As the population matured over the years, the average length and mass of captured snakeheads increased. In addition, these fish fed primarily on the local aquatic fauna population, decreasing the amount of game fish for local anglers.