Snakeheads are not as bad as people portray them.
Northern Snakehead can be found in the Potomac River and surrounding rivers. Yes, they are slowly spreading. However, anecdotal observations from area anglers suggested that Largemouth Bass fishing as remained stable and even improved in certain areas after the discovery of Northern Snakehead in 2002. It is at least not harming the Largemouth Bass population. Snakehead prey predominantely on Banded Killifish (most important by number) and Bluegill (most important by weight). Banded Killifish usually average around 2-3"...so even though Bluegill is most important by weight, Northern Snakehead does not have as significant impact on Bluegill.
http://fishwild.vt.e...heads/diet.html
Bluegill Sunfish and Largemouth Bass were non-native and introduced into the Potomac watershed anyways...can't exactly say that Northern Snakehead are affecting NATIVE population.
http://www.potomacri...ishList0213.pdf
I do feel some sympathy for the native killifish species such as Mummichog and Banded Killifish.
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As for the Great Snakehead (aka Bullseye or Cobra Snakehead), according to the biological administrator of the FWC's non-native fish research lab in Boca Raton:
"Gestring said the FWC also considers the bullseye snakehead permanently established in Northwest Broward. Scientists expect they will eventually escape into the Everglades but believe the warm-water species probably wouldn’t survive north of Orlando.
In the Northwest Broward canal system, they don’t appear to have wreaked ecological havoc, Gestring said. After a decade, there is no sign they’re doing any more damage than 22 other foreign fish that also have settled in Florida’s freshwater canals and lakes.
'What we’re seeing is that the native fish population seems to be holding strong,’’ he said. “We’ve not been able to detect any measurable impacts by bullseye snakeheads on any of our individual native species.'"
http://www.miamihera...ous-record.html
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Blotched Snakehead was also introduced intentionally in Hawaii as a food fish at the time due to its popularity. The species was introduced into a reservior created for flood control and irragation. Within this lake was an established population of Bluegill, Largemouth Bass, Smallmouth Bass, Channel Catfish, Blotched Snakehead and Common Carp, until a bloom of invasive Salvinia molesta plant choked out all the sunlight in the reservior and caused a crash in the fish population. Today, the lake supports a population of Butterfly Peacock, Largemouth Bass, Smallmouth Bass, Bluegill, Channel Catfish, Sailfin Catfish, Blotched Snakehead, Freshwater Needlefish, Tilapia species, Red Devil, Banded Jewel Cichlid, Oscar and many other species at smaller number. There was a report of Suribim Catfish and even Redtail Catfish in the lake.
The Blotched Snakehead population is quite small now. I have seen one, but it was very wary and it didn't even entertain to look at my 2" white senko. They are not even close to affecting the other fish population in the lake. Other invasives like the Banded Jewel Cichlid and Red Devil are creating more of an issue.
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I have fished for Northern Snakehead in the Potomac as well as Cobra Snakehead in these northern Broward county canals. I can tell you that they are much more wary and much less aggressive than people preceived them. I find them much more fun to chase than Largemouth Bass. In fact, one morning on the Potomac, my friend and I caught over a dozen bass without trying while targetting Northern Snakehead and we only caught 2 Northern Snakeheads. I also caught a few Largemouth Bass in the Broward canals easily while only getting a few missed strikes from the Cobra Snakehead. If you actually observe the two snakehead species, you'll find that they are mainly ambush predators that are very wary of movements above or from shore. They will readily abandon their ambush sites if they sense the presense of other large animals nearby.
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I love hunting Snakeheads. I love their willingness to strike a topwater lure. If they were to establish in Ontario, they should have minimal impact if the Potomac River is of any indication. I do feel sympathy for the native Bowfin since their behaviour, apparence and habitat is so similar that people would mistaken Bowfin for snakehead (as it happens in Florida and Potomac River) such that people would kill Bowfin by accident. Snakehad could also compete for habitat with Bowfin.
Shhh...don't tell anyone. I'm not introducing them myself...that would be wrong...and I am not suggesting anyone should do it at all...don't get me wrong.
Now...for the smaller native species like the topminnow and killifish, that may be an issue with so many hungry cichlids around. SoFLA is such a cool place to fish though...you can catch fish from 5 continents quite possibly in the same area (Florida Gar from North America, Oscar from South America, Spotted Tilapia from West Africa, Walking Catfish from Asia, Common Carp from Europe)! We need some representation from Australia...maybe Barramundi 
They are brackish just like snook...and wait...there already is a barramundi farm in Osceola...just a matter of time. 
