Tuesday, October 31, 2017 by Rhonda Johansson
Officials in the city of St. Albert in Canada say that they are in a “battle” against overlarge Asian goldfish that were released into the wild four years ago. These gigantic invasive species have quickly grown into a school of more than 4,000 and are noted to be extremely aggressive. These “monster” goldfish can grow to about 12 inches and have now infested Edgewater Pond.
City crews discovered the problem roughly two years ago when they tried to scoop all the fish out with nets but could not. St. Albert’s environment director Leah Kongsrude said that these fish “[may look] really cute…in your little glass bowl, but you let them out and they turn into monsters.”
In the fall of 2015, Kongrude and her team partially drained the pond in the hopes that the remaining water would freeze, killing the rest of the fish. This did not happen, however. The goldfish merely adapted to the decreased water levels and temperature. Undeterred, park officials tried an experimental treatment called “electrofishing.” This is where they would run a current in the water, with a voltage that was strong enough to stun the fish (but not kill them). Officials would then be able to remove the pests without trouble. Needless to say, the current did nothing.
“The battle goes on,” Kongsrude said. “I think of zombie movies when I think about [how] we froze the storm pond right to the bottom and they survived through that, when we tried to electro-fish [them] it didn’t do anything.”
St. Albert officials decided earlier this year in September that they would use the organic pesticide, rotenone. Supposedly, this pesticide does not harm other animals and plants, although this has yet to be verified. The results, though, speak for themselves. After only a week of treatment, officials pulled out 4,000 dead goldfish.
Kongsrude said that drastic measures needed to be taken now before the giant goldfish could spread to the Sturgeon River and disturb the ecosystem by out-competing native species for food. What made the “fraken-fish” even more dangerous was that they were not endemic to the region, so there were no natural predators that could stop the population growth.
Kongstude said that they are planning on spraying the pond with rotenone for a few more weeks just to ensure that the goldfish stay dead.
Rotenone is a controversial pesticide. On one hand, it is an organic substance, derived from naturally occurring chemicals found in roots, seeds, and leaves of subtropical plants. It is a commonly used and highly popular pesticide among fishermen as it is non-selective. This means that rotenone has the potential to kill any fish that is exposed to it. It is alleged to be “safe” because it does not bioaccumulate and dissolves easily in water.
However, there have been several studies which have linked rotenone exposure to the increased risk of developing Parkinson’s disease. The American Fisheries Society says that more evidence is needed to fully validate this claim.
The National Institute for Occupational Safety and Health (NIOSH) does note that the powder can cause labored breathing, sore throat, and unconsciousness if inhaled. Direct exposure to rotenone is also linked to skin inflammation and eye damage. The group also noted that the substance “may cause long-term effects in the aquatic environment.”
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