Hello, Readers!
After so many blue moons, I'm finally bringing you guys an entire post that covers the invasive Northern Snakehead Species in the USA (Channa argus), which has been an extremely exciting topic in the fishing community since 2002 (and upsetting for some).
August 3rd, 2012 - Leo S. with a small Northern Snakehead (Channa argus) from Newton Lake, NJ.
During these last 3 years that I've been active in the local fishing community, I've heard way too much about Northern Snakeheads: I've heard about it from fellow anglers, from the general public, from the media (TV and online articles), not to mention that I've seen multiple threads on Northern Snakeheads in different fishing forums (most of them end up in fights because of divided opinions and tons of headache because of biased information on the same).
Summarizing all of that - the opinions in the fishing community are always divided in two sections: on one side, there's a part of the community that views this Species of fish as a danger to our aquatic ecosystems and "native fishes" (in quotes, because many anglers don't really understand the definition of a fish being native to a certain body of water); therefore, they kill every single one of them and they firmly support their eradication. On the other side, there's a part of the community that believes that Northern Snakeheads can no longer be eradicated, especially because they are already in open bodies of water (i.e. Delaware River, Schuylkill River, Potomac River); therefore, they are willing to accept this Invasive Species as a "game fish" (in quotes, because the term sport fish/game fish is really relative) and they support the no-harvest idea for Northern Snakeheads.
Every time I post a photo of a Northern Snakehead on this fishing blog or my fishing page on Facebook, aggressive e-mails and responses start to come in (i.e. "Kill them! They are destroying our ecosystems!") Even nowadays, I still receive some e-mails from time to time concerning Northern Snakeheads: people ask me about my opinion on their impact; where do I fish for them around Philadelphia and South Jersey; which "side" do I stand with; etc.The e-mails are imminent; after all, it's quite obvious that many people, including members of the fishing community, still don't know enough about them. Northern Snakeheads are, indeed, a new Species of fish in our bodies of water and they have been around Philadelphia and South Jersey for less than a decade or so (the last reports of it were in the John Heinz National Wildlife Refuge [1]). Therefore, I've decided to write this post because (1) I'm sick tired of listening to all the online biased information on Northern Snakeheads every time I go to a fishing forum or every time I post a photo of it, and (2) I would like to express my opinions on this topic, which are solely based on recent scientific studies and data results concerning this Species of fish.
In other words, you are about to read a post on Northern Snakeheads that is entirely based on scientific data and online articles. I've decided to make it so formal that I'm even including references at the end of this post! Of course not every cited source is scientifically accurate; however, not every piece of information is false neither: the accuracy of each source is up to the readers' discretion and knowledge. Therefore, before expressing your own opinion on this topic, I encourage you to read through all the recent scientific studies and articles regarding Northern Snakeheads that are portrayed further below. After all, it's always good to know the facts before expressing oneself.
Notice that this post is directed mainly to the fishing community in Philadelphia and South New Jersey. After all, my fishing blog - "Extreme Philly Fishing" - focuses mainly on these locations. However, I'm also trying to make it as educative as possible for the open public! So, even though I'm using local examples and emphasizing on a single Species of the Channidae family, I'm leaving the knowledge out there for anyone who wishes to know more about Snakeheads.
After you read this whole post and its references, you will become a "Northern Snakehead Expert" yourself; therefore, you will eventually be able to differ biased information from scientific information, doesn't matter where you read it from.
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Note 1: I know that not everyone is familiar with the reference notation. Therefore, let me briefly explain it: every time you see a "[*]" in the text, scroll all the way to the end of the post to find its reference source. Using the "[*]" notation just means that I took that piece of information in my paragraph from such source.
Note 2: There are many "side notes" on this post. Side notes consist mainly of curiosities and additional information that may help the reader understand more about the main topic.
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Here is something that you probably didn't know: Northern Snakeheads do jump from time to time.
Notice that this post is directed mainly to the fishing community in Philadelphia and South New Jersey. After all, my fishing blog - "Extreme Philly Fishing" - focuses mainly on these locations. However, I'm also trying to make it as educative as possible for the open public! So, even though I'm using local examples and emphasizing on a single Species of the Channidae family, I'm leaving the knowledge out there for anyone who wishes to know more about Snakeheads.
After you read this whole post and its references, you will become a "Northern Snakehead Expert" yourself; therefore, you will eventually be able to differ biased information from scientific information, doesn't matter where you read it from.
---
Note 1: I know that not everyone is familiar with the reference notation. Therefore, let me briefly explain it: every time you see a "[*]" in the text, scroll all the way to the end of the post to find its reference source. Using the "[*]" notation just means that I took that piece of information in my paragraph from such source.
Note 2: There are many "side notes" on this post. Side notes consist mainly of curiosities and additional information that may help the reader understand more about the main topic.
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Since this is a HOT topic in the fishing community even nowadays, it requires a lot of writing. So, I've decided to divide this post in four main parts:
1. The History and Introduction of Northern Snakeheads in the United States of America
2. The Myths Pertaining Northern Snakeheads and Some Solid Facts about this Species
3. The Known Impact of Northern Snakeheads in our Aquatic Ecosystems Up to Date
4. The Future of Northern Snakeheads: Acceptance or Denial in the Fishing Community?
--- The History and Introduction of Northern Snakeheads in the United States of America ---
In this portion of the post you will learn about (1) how Northern Snakeheads were first introduced in the USA, and (2) their history since 2002 until 2013, giving emphasis to Philadelphia and its surroundings.
First, for a brief introduction on this Species of fish, you may access its Wikipedia page here. Note that Wikipedia pages are by far the most trustful sources of information; however, they are a very good source when it comes to familiarizing oneself with a certain field. In other words, they are a very good start if the person has absolutely no idea of the topic he/she is looking for.
If you already read its Wikipedia page, you should know by now that Northern Snakeheads are native to Asia -- mainly Northern China and Eastern Russia. In other words, naturally, they should not be here. You should also know the basics of its anatomy and physiology; and how they were "first" introduced in the United States of America (in quotes, because Wikipedia is wrong about the first introduction being in Maryland). Since the first big known occurrence of an invasive Species is usually one of the most important ones, it's good for us to dig deeper into the "Crofton incident."
According to Wikipedia, the first Northern Snakehead appearance was in Crofton Pond -- Maryland, during the Summer of 2002. Indeed, the first record of a Northern Snakehead in Maryland was obtained by the government office in Annapolis, when a fisherman appeared with a photo of a strange fish that he caught and released at Crofton Pond [2].
As a matter of fact, even though this wasn't the first recorded case of a Northern Snakehead caught in the USA, one can say that the Crofton incident was the beginning of our awareness regarding Northern Snakeheads and their impact: that event was the main trigger to all the attention that this Species of fish has been receiving in the media, in the public, and even in politics.
The first recorded case of a Northern Snakehead in USA waters happened on August 22nd, 1997: a Northern Snakehead (Channa argus) was collected through electrofishing in Silverwood Lake, a reservoir in California. It measured 29 inches and 7.5lbs [3]. Eventually, that wasn't the only occurrence: there were many other registered cases of Northern Snakeheads here and there, prior to 2002. However, the big deal about the Crofton incident was that Crofton Pond was a closed body of water; therefore, we were finally able to realize that Northern Snakeheads were able to breed on their on accord, in the wild -- an important factor regarding any invasive Species of fish.
The first recorded case of a Northern Snakehead in USA waters happened on August 22nd, 1997: a Northern Snakehead (Channa argus) was collected through electrofishing in Silverwood Lake, a reservoir in California. It measured 29 inches and 7.5lbs [3]. Eventually, that wasn't the only occurrence: there were many other registered cases of Northern Snakeheads here and there, prior to 2002. However, the big deal about the Crofton incident was that Crofton Pond was a closed body of water; therefore, we were finally able to realize that Northern Snakeheads were able to breed on their on accord, in the wild -- an important factor regarding any invasive Species of fish.
After such discovery, Northern Snakeheads were immediately classified by the local government as a treat, even though little research was performed on them at the time, back in 2002. They were defined as "a voracious top-level predator [4]," and even the National Geographic, a magazine that I deeply appreciate, started to throw out the myth that they were able to travel long distances on land and breathe air for a long period of time [5] (see section number 2 of this post for more details on how these are myths). Consequently, the public, the fishing community, and the government all feared that they would heavily impact our aquatic ecosystems in a very negative way.
Therefore, the governmental agencies immediately took action:
They first surveyed Crofton Pond and its surrounding bodies of water (3 ponds in total). They first drained Crofton Pond, eradicating all Species of fish there (including Northern Snakeheads) [6]. Of course, that wasn't nearly enough for the government, since they still feared that the Snakeheads could have been established in the surrounding bodies of water through floods, after heavy periods of rain. So, regarding the 3 surrounding bodies of water, they first applied the herbicides Diquat Dibromide and Glyphosate (Rodeo) to decrease the oxygen levels in those ponds, inducing a fish kill. As expected, numerous Species of fish died due to the low amount of oxygen. Even so, after two weeks and lots of dead fish, they applied the piscicide "rotenone," eradicating not only the Northern Snakeheads in those closed bodies of water, but all the other Species of fish as well [7].
Therefore, the consequences for "eradicating" a single Species of fish actually cost the life of all the remaining Species (i.e. Largemouth Bass, Sunnies, Carp, Catfish, etc). Looking from a "local" point of view, many small ecosystems were destroyed in order to kill a single type of fish. In other words, at least 4 ponds in Crofton were left lifeless.
This touching and cruel story leads us to our fist question: how exactly did everything start? Why were Northern Snakeheads - a fish native to Asia - in the Crofton Pond; a closed body of water?
The answer to that question was rather simple: the Snakeheads were released in the pond by an owner that no longer wanted them. The original story came up just a couple months after Crofton Pond made to the national news, around July of 2002:
Two years prior to their discovery, a Crofton resident ordered a couple live Northern Snakeheads from New York, planning to make a soup for his ill sister. Being originally from Hong Kong, this resident believed in the curative properties of this fish [8]. However, his sister was already well once the live fish batch arrived; therefore, without the need of making the soup, the owner placed these fish inside a fish tank. He fed them some Goldfish once in a while and they eventually started to grow. Once they started to eat as much as 12 Goldfish per day, the owner finally decided to get rid of them: he threw his pets in the Crofton Pond [9].
That's how Northern Snakeheads first made their way to Crofton Pond: from Asia to a fish market in New York, then to the household of the Crofton resident, and finally to the pond. A long journey, isn't it?
As a matter of fact, Northern Snakeheads were available for purchase at different Asian markets prior to 2002. Anyone could purchase one at that time, even you! Being a delicacy in Asia, the fish was heavily imported in the USA for human consumption purposes. However, after the Crofton incident and the realization of how dangerous they could be to our native ecosystems at the time, the U.S. fish and wildlife service (USFWS) finally prohibited its importation and interstate transportation under the "Lacey Act, 18 U.S.C. 42." [10]
As mentioned before, even prior to the incidents in Maryland, minor occurrences of Northern Snakeheads were already present here and there: in California, Massachusetts, Florida, and North Carolina [11]. However, those never even made to the news! Even in the Potomac River, after further research on Northern Snakeheads, biologist John Odenkirk from the Virginia Department of Game and Inland Fisheries was able to come to the conclusion that those fish were present prior to 2002; prior to the Crofton incident. [12]
Therefore, emphasizing, the Crofton incident in 2002 attracted all of our attention to Northern Snakeheads and their ability to reproduce in our local environments; however, many appearances of this Species of fish in public waters were already seen prior to 2002. And after 2002, the Northern Snakeheads started to "spread" (in quotes, because different Northern Snakeheads were released in different states) around different states.
And, in 2004, the same Species of fish "appeared" in our area - Philadelphia. Nobody knows exactly when they were released, or for how long Northern Snakeheads have been living in Meadow Lake, which is located in South Philadelphia (The Franklin Delano Roosevelt Park -- FDR). However, the first recorded samples were collected in July of 2004 [13].
Apart from the outrageous "Voracious Top-level Predator" nickname, Philadelphians started to refer to it also as "Frankenfish" - a term based on the 2004 "Frankenfish" movie, which was then based on the Crofton Pond incident in Maryland [14]. Isn't it interesting how the public can relate a fictional movie to the spread of Northern Snakeheads in the USA?
Since then, there have been occurrences of Northern Snakeheads in the lower Schuylkill River and the Delaware River [15]. The latest occurrence in PA happened in March of 2012, where a sample was collected at the John Heinz Wildlife Refuge [16]. Taking in consideration that they are already swimming in open waters, the PA Fish and Boat Commission is not taking radical measurements to eradicate them. According to their staff, they are currently only monitoring the surrounding waters [17]. It's also important to note that after they made their way to the open waters of the Schuylkill and Delaware Rivers, they also started to migrate over the creeks and river systems in South Jersey - mainly tributaries of the Delaware River [18].
Nowadays, they can be found in many different locations around us, including:
Note: click on the links to be redirected to the USGS monitoring website.
PA (Philadelphia):
April 14th, 2012 - Mike H. with a Northern Snakehead from Meadow Lake (FDR Park, South Philadelphia)
July 3rd, 2012 - Mike H. with a Northern Snakehead from the tidal Schuylkill River (Center City, Philadelphia)
Here is a video of Northern Snakehead fry in Meadow Lake, Franklin Delano Roosevelt Park, Philadelphia.
New Jersey (mainly South NJ):
June 26th, 2013 - Leo S. with a juvenile Northern Snakehead from Newton Lake (Collingswood, NJ)
May 20th, 2013 - Leo S. with an adult Northern Snakehead from Newton Lake (Collingswood, NJ)
Concluding this section of the post: you should now know about (1) how Northern Snakeheads were first introduced in the USA, and (2) the history of their spread from 2002 until now, giving emphasis to Philadelphia and its surroundings.
A little summary of these two main topics is below:
(1) Northern Snakeheads were first introduced in our water as released "pet-fish." Prior to 2002, they could be purchased "live" in different Asian markets for human consumption purposes, especially since they were considered to be an Asian delicacy with healing properties.
(1) Northern Snakeheads were first introduced in our water as released "pet-fish." Prior to 2002, they could be purchased "live" in different Asian markets for human consumption purposes, especially since they were considered to be an Asian delicacy with healing properties.
(2) There were minor occurrences of these fish around the country prior to 2002 (including the Potomac River); however, it was the Crofton incident in Maryland that triggered our attention towards them. Giving emphasis to Philadelphia and its surroundings, the first registered occurrences of Northern Snakeheads happened back in 2004, at Meadow Lake (FDR Park). Since then, this Species of fish made their way to open bodies of water - the Schuylkill (occurrences dating back to 2008) and the Delaware River, and are currently migrating to different tributaries of the same (i.e. Audubon, Rancocas, and Newton - South New Jersey).
--- The Myths Pertaining Northern Snakeheads and Some Solid Facts about this Species ---
In this section of the post, you will learn about (1) the main Northern Snakehead myths that were created by the public and the media, and (2) a couple solid facts about this invasive Species of fish, all based on scientific studies and accounts of experts in the field.
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Side note:
Before anything else, I would like to make a side note: there are currently 29 known Species of Snakeheads (Channidae) - 26 native to Asia and 3 native to Africa [19], and the Northern Snakehead (Channa argus) is only ONE of them. Therefore, be careful not to get confused while reading research papers and online articles: some of them talk about the characteristics of the overall family (Channidae) whereas others focus specifically on Northern Snakeheads (species - Channa argus). It's good to mention that there are currently two Species of Snakeheads in our waters that are invasive and able to reproduce: the Northern Snakehead (Channa argus) and the Bullseye Snakehead (Channa marulius) [20]. However, this post is mainly focusing on Northern Snakeheads, since Bullseye Snakeheads are most active in Florida.
It is important for the reader to know about this "genus and species" concept because, for example, some Species of the Channidae family were proven to be able to walk on land [21]; however, the Northern Snakehead and the Bullseye Snakehead have been proven to not be able to do so [22].
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Side note:
Before anything else, I would like to make a side note: there are currently 29 known Species of Snakeheads (Channidae) - 26 native to Asia and 3 native to Africa [19], and the Northern Snakehead (Channa argus) is only ONE of them. Therefore, be careful not to get confused while reading research papers and online articles: some of them talk about the characteristics of the overall family (Channidae) whereas others focus specifically on Northern Snakeheads (species - Channa argus). It's good to mention that there are currently two Species of Snakeheads in our waters that are invasive and able to reproduce: the Northern Snakehead (Channa argus) and the Bullseye Snakehead (Channa marulius) [20]. However, this post is mainly focusing on Northern Snakeheads, since Bullseye Snakeheads are most active in Florida.
It is important for the reader to know about this "genus and species" concept because, for example, some Species of the Channidae family were proven to be able to walk on land [21]; however, the Northern Snakehead and the Bullseye Snakehead have been proven to not be able to do so [22].
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As I mentioned in the first part of this post, Northern Snakeheads were classified as a threat soon after its discovery in Crofton Pond, MD. Just a couple months after the incident, there was already a kind of mass hysteria phenomenon among fishing communities, the general public, and even certain governmental agencies!
After the Crofton incident, people were so afraid of the Northern Snakeheads that certain "myths" started to circulate in the media. Dr. Paul Shafland - a Florida fisheries biologist with more than 30 years of experience in the field of exotic fish species - described this hysteria phenomenon very well:
"Unfortunately, the public is reading, hearing, and seeing reports describing these fishes as 'Frankenfish' or 'fish from hell'...According to some accounts, this alleged monster eats anything in its path, can walk on land, survive up to three days out of water, and will even attack and kill people when guarding its young!" [23]
It certainly sounds like a monstrous creature directly out of a Hollywood movie, isn't it? And as briefly mentioned before, it just so happened that Hollywood was so interested in peoples' fear of the Northern Snakeheads that the movie "Frankenfish" was made in 2004 (about biologically engineered Snakeheads that murder people - watch it for more details). This is one clear example of why we should never believe in everything that is out there, unless there's sufficient evidence to support the claims.
Therefore, below are some of the main myths concerning Northern Snakeheads. Each one of the claims is followed by a scientific explanation, giving you the amount of rightfulness and wrongfulness that it holds. So, let's debunk some of them!
1. "Northern Snakeheads are voracious fish that will eat anything in its path, eventually wiping out native fish communities"
No, they don't. Recent scientific studies have showed that they are mostly a very shy and "lazy" type of fish when it comes to their feeding behaviors [24], and the "aggressively" and "voracious" adjectives are nothing but exaggerations by the media and the public's mass hysteria [25].
Northern Snakeheads are classified as "lie-in-wait" Predators. According to the branch of ichthyology (the study of fish), there is a classification for freshwater fishes depending on the shape of their bodies and their feeding patterns: the rover predators (i.e. Largemouth Bass, Trout, Walleye), the lie-in-wait predators (i.e. Pickerel, Gar, Northern Snakehead), deep-bodied fish (Sunfish and Buffalofish Species), eel-like fish (Eel and Lampreys), bottom clingers (Sculpins and Darters), bottom rovers (Catfish and Sucker), and surface-oriented (Killifish and Mummichogs) [26].
In other words, the preferable feeding pattern for Northern Snakeheads is to hang around cover and ambush easy targets that pass by. In tidal waters, they tend to hold particularly close to the outgoing current, ready to attack on prey that are being pushed out by the tide [27]. Pre-spawn and post-spawn are the only times of the year when they feed more actively, roaming in the shallows or in open water in search of food [28].
Therefore, Northern Snakeheads definitely do not eat everything in their way. As mentioned above, they tend to eat only small fishes and easy preys that pass on top of their heads, not to mention that they would never eat a fish that is more than 33% of their body lengths [29], [30]. Despite what the fishing community believes in, they will never attack targets that are the same sizes as them, unless it's their spawning season and other Species of fish approach their nests to eat their eggs or young (in a way, every fish would attack another fish to defend their young) [31].
Northern Snakeheads are classified as "lie-in-wait" Predators. According to the branch of ichthyology (the study of fish), there is a classification for freshwater fishes depending on the shape of their bodies and their feeding patterns: the rover predators (i.e. Largemouth Bass, Trout, Walleye), the lie-in-wait predators (i.e. Pickerel, Gar, Northern Snakehead), deep-bodied fish (Sunfish and Buffalofish Species), eel-like fish (Eel and Lampreys), bottom clingers (Sculpins and Darters), bottom rovers (Catfish and Sucker), and surface-oriented (Killifish and Mummichogs) [26].
In other words, the preferable feeding pattern for Northern Snakeheads is to hang around cover and ambush easy targets that pass by. In tidal waters, they tend to hold particularly close to the outgoing current, ready to attack on prey that are being pushed out by the tide [27]. Pre-spawn and post-spawn are the only times of the year when they feed more actively, roaming in the shallows or in open water in search of food [28].
Therefore, Northern Snakeheads definitely do not eat everything in their way. As mentioned above, they tend to eat only small fishes and easy preys that pass on top of their heads, not to mention that they would never eat a fish that is more than 33% of their body lengths [29], [30]. Despite what the fishing community believes in, they will never attack targets that are the same sizes as them, unless it's their spawning season and other Species of fish approach their nests to eat their eggs or young (in a way, every fish would attack another fish to defend their young) [31].
A good part of the fishing community, especially Bass anglers, tend to believe that the Northern Snakeheads will deplete the Largemouth Bass population, not to mention the other Species of Game Fish. However, that's totally biased. According to the research done by a group of experts in the field, 27% of the diet of a Northern Snakehead consists solely of Banded Killifish (Fundulus Diaphanus) - their primary target. Depending on the body of water, the rest of their diet consists of: 5% of White Perch (Morone Americana), 5% of Pumpkinseed (Lepomis Gibbosus), and 5% of Bluegills (Lepomis Macrochirus) [32].
The Largemouth Bass (Micropterus Salmoides), for example, consists only of 1% of their diet. In other words, the number of Largemouth Bass fingerlings in Northern Snakehead's stomachs were much much lower in comparison to other Species of fish. Other "native" Game fish species are even below the 1% range, including the Channel Catfish (Ictalurus Punctatus) [33].
One could say as an argument that Northern Snakeheads are competing for food with other "native" Species of Game fish - say for example the Largemouth Bass - which is bad for our "native" fishes. However, it's been known for a while that Northern Snakeheads are mainly piscivorous, and sometimes they will even eat fingerlings of their own kind [34]. Largemouth Bass, on the other hand, have been proven by research to have a good amount of frogs, turtles, small snakes, and crayfish in their diet [35]. Therefore, even though we are comparing the diets of Largemouth Bass in relationship to Northern Snakeheads, single-handed depletion of sources by Northern Snakeheads is something that has not yet been proven [36] (also, despite what lots of anglers believe in, frogs, small mammals, etc, consist only of <1% of a Snakehead's diet in comparison to fish)
The worst and most realistic case scenario for the depletion of a whole small ecosystem, single-handed by Northern Snakeheads, would be to place them in a closed body of water that (1) lacks a top piscivore, and (2) has some rare and small Species of fish. Then, that would be truly disastrous [37]. Otherwise, Dr. Paul Shaftland, Walter Courtenay, Jon Fury, and Jeffrey Hill -- four experts in Northern Snakeheads -- state: "it's an exaggeration to say that Northern Snakeheads can single-handedly deplete native fish communities [38]".
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Side note:
Lastly, on a side note, I would like to comment on the definition of a "native" Species of fish, since I've been putting this term in quotes throughout this post. Not all anglers in the local fishing community have a good idea idea of what it means for a fish to be native or invasive to a certain body of water. After all, the definition of "native" is very vague over time.
For example: the Largemouth Bass (Micropterus salmoides), Common Carp (Cyprinus carpio), and Channel Catfish (Ictalurus punctatus) in the Potomac River are all Invasive Species of fish that were introduced in the past century [39]. So, for instance, if Northern Snakeheads were consuming those fish, should I not care because it would be eating other Invasive Species of fish? Being invasive or not, I would definitely be sad if Northern Snakeheads were eating those Species of fish all around.
Another example: White Perch (Morone americana) have been shown through several studies to cause trouble in different ecosystems by being an introduced invasive Species [40].
A local example: Flathead Catfish (Pylodictis olivaris) are still an invasive Species to the Schuylkill River and many people believe that the decrease in Smallmouth Bass population (Micropterus dolomieu) is due to them; however, there are no current scientific studies that show that. Despite all of that, a lot of anglers have taken a liking to the Flatheads and are currently "CPRing" them (Catch-Photo-Release), even though they are still an invasive Species - theoretically speaking. As for today, the biggest recorded Flathead Catfish from the Schuylkill River measured 55lbs, breaking the state record by 7lbs or so. However, the fish was not weighted at an official station. It was released and it's still swimming in the Schuylkill River for someone else to catch it!
Chris McIntee with his 55lbs Flathead Catfish from the Schuylkill River.
Another side note: about 10 years ago, when Flathead Catfish were first found in the non-tidal Schuylkill River, the PA Fish and Boat Commission was highly enforcing their eradication [41]. Nowadays, several local fisheries biologists state that it's okay to not kill them.
And, finally, one of the most absurd cases in my eyes is the Green Sunfish (Lepomis cyanellus) being invasive in New Jersey. By law, I have to kill the Green Sunfish every time I catch one. It really hurts me to do so because I really love them. For me, they are just small "Sunnies" with a beautiful coloration. But according to the local agencies, they are invasive; therefore, they must be eradicated.
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2. "Northern Snakeheads can walk and travel long distances on land, making overland migrations"
This one is another absurd myth that we must debunk right away. During these past years in Philadelphia, I've heard numerous local anglers tell me that "Northern Snakeheads propagated in Meadow Lake by hopping from pond to pond." This always reminded me of grasshoppers, seriously.
Since the FDR Park (Franklin Delano Roosevelt) consists of a set of ponds, certain anglers still truly believe that Snakeheads are present in all of them because they had the unique ability to "walk through land." In other words, they were able to do overland migrations.
On one hand, just like certain other Species of fish (i.e. Bowfin), the Northern Snakehead can move through very shallow water, swamps, and even very moist mud. On the other hand, they would only be able to flop and squirm on dry land, barely making their way back to the water [42].
The reason is simple and quite obvious when it comes to fish anatomy and physiology: just like most fishes, they have pectoral fins that lack spines (having only soft rays). Therefore, they have no means of propelling themselves forward in dry land [43].
There are closely 30 Species of Snakeheads in Asia, and some of them are known for being able to travel short distances in moist mud, under very specific circumstances. According to Dr. Walter Courteney -- ichthyologist and fisheries biologist -- such land movements by Snakeheads “must occur during the monsoon season so snakeheads can keep their bodies and breathing organ moist or else these fish will die in a matter of hours, not days! [44]”
Therefore, Northern Snakeheads do not walk on land, and they don't have the ability to do overland migrations -- at least not with the conditions that we have here. As a matter of fact, a Walking Catfish, or even an Americal Eel, has a better ability of walking on dry land [45].
Therefore, the best two means of propagation for Northern Snakeheads are human transportation and migration through floods, after heavy periods of rain (which is probably how they spread in Meadow Lake). Notice that human transportation of live Northern Snakeheads is strictly illegal nowadays; in other words, theoretically, their recent propagation to the Schuylkill, Delaware, and even South New Jersey is probably due to migration and floods.
This one is another absurd myth that we must debunk right away. During these past years in Philadelphia, I've heard numerous local anglers tell me that "Northern Snakeheads propagated in Meadow Lake by hopping from pond to pond." This always reminded me of grasshoppers, seriously.
Google Earth's view of the FDR Park in South Philadelphia. Five of the six bodies of water are public (1-5), leaving the 6th one private to a local golf club. Bodies of water 1, 2, and 4 are interconnected, leaving 3, 5, and 6 as "closed" bodies of water. Even so, Northern Snakeheads can be found in all of them nowadays.
Since the FDR Park (Franklin Delano Roosevelt) consists of a set of ponds, certain anglers still truly believe that Snakeheads are present in all of them because they had the unique ability to "walk through land." In other words, they were able to do overland migrations.
On one hand, just like certain other Species of fish (i.e. Bowfin), the Northern Snakehead can move through very shallow water, swamps, and even very moist mud. On the other hand, they would only be able to flop and squirm on dry land, barely making their way back to the water [42].
The reason is simple and quite obvious when it comes to fish anatomy and physiology: just like most fishes, they have pectoral fins that lack spines (having only soft rays). Therefore, they have no means of propelling themselves forward in dry land [43].
There are closely 30 Species of Snakeheads in Asia, and some of them are known for being able to travel short distances in moist mud, under very specific circumstances. According to Dr. Walter Courteney -- ichthyologist and fisheries biologist -- such land movements by Snakeheads “must occur during the monsoon season so snakeheads can keep their bodies and breathing organ moist or else these fish will die in a matter of hours, not days! [44]”
Therefore, Northern Snakeheads do not walk on land, and they don't have the ability to do overland migrations -- at least not with the conditions that we have here. As a matter of fact, a Walking Catfish, or even an Americal Eel, has a better ability of walking on dry land [45].
Therefore, the best two means of propagation for Northern Snakeheads are human transportation and migration through floods, after heavy periods of rain (which is probably how they spread in Meadow Lake). Notice that human transportation of live Northern Snakeheads is strictly illegal nowadays; in other words, theoretically, their recent propagation to the Schuylkill, Delaware, and even South New Jersey is probably due to migration and floods.
3. "Northern Snakeheads can breathe air and stay alive outside of the water for up to three days"
This is another myth that circulates around the public and the fishing community because of its gross exaggeration by the national media. I can understand how people would be afraid of certain characteristics of the Northern Snakehead because of the lack of scientific evidence in the field nowadays; however, this claim can be debunked with simple fish anatomy and physiology -- knowledge that we already have in our hands!
--
Side note:
The paragraph above is a very good example to support the idea that education and curiosity are both very important factors when it comes to sorting out what is true, what is false, and how much do we take for granted when it comes to a source or piece of information.
I would like to quote something that one of my Math Professors said one day, regarding primary sources (click to be redirected to Wikipedia for its definition):
"Opinion and belief should live in the absence of fact, not in place of it. With so much garbage out there, it's our responsibility to fact check ourselves. Herein lies the problem: we don't usually fact check, and when we do, really getting to the facts is becoming increasingly difficult when everything is packaged in opinion with no reference to a primary source. Advice: if you can't verify something with a primary source, don't consider it fact. You will do everyone a favor."
Even though he's a former Mathematics professor, those words are pretty deep. So, think about it! Did you ever reach primary sources for this Snakehead myth, for example? (i.e. an artifact, document, recording, or other source of information at the time under study)
--
Scientifically speaking, Northern Snakeheads do have the ability to "breathe air;" however, as Dr. Courtenay, Fury, Hill, and Shafland indicate once again: "suggestions that these fish can live without water for up to three days is a gross exaggeration [46]."
I'll go with the "a picture is worth a thousand words" approach here to debunk this myth:
Do not panic if you did not understand this picture at a first glance. I'll explain:
Different than most types of fish, Northern Snakeheads do "breathe air." This interesting ability is due to the suprabranchial chamber (see it in the picture above), which is actually a series of small spaces that are located in the back portion of their head. On a magnified view -- the pink park on the bottom of the picture (epibranchial respiratory fold), one can see that these spaces are filled with folded tissues with high surface areas. These folded tissues allow the Snakeheads to exchange oxygen directly from air to their blood [47].
--
Side note:
Here's the catch, though: this is science, and not magic. Something extra is needed in other to transfer oxygen from one medium to another (click to be transferred to the definition of medium). For example: we -- human beings -- need our diaphragm in order to breathe and our alveoli in order to exchange carbon dioxide for oxygen.
Not only the diaphragm divides our thoracic cavity (lungs, heart, etc) from our abdominal cavity (stomach, intestines, etc); it allows air to flow in our lungs as it contracts. In other words, the diaphragm plays a fundamental role in human respiration: as it contracts, our thoracic cavity's volume increases, allowing air to flow from outside into our lungs. Once it retracts, our thoracic cavity's volume decreases, and then the air flows from our lungs to the outside. This is basically the concept of inhaling and exhaling that every college student goes through in a Biology class (Human Anatomy and Physiology), and it's inside the lung where we exchange our body's carbon dioxide with fresh oxygen.
--
Snakeheads, however, do not have a diaphragm to help them breathe air. Instead of that, they have the suprabranchial chamber that I described above. Instead of having alveoli to exchange carbon dioxide for oxygen and vice-versa, Snakeheads use water: during each breath, the water in the surface area of the folded tissues in the chamber allows oxygen to be absorbed by the fish, directly into their bloodstream [48]!
Thus, their ability to breath air is very limited. So, even when Northern Snakeheads are completely outside of the water, they still depend on water to breathe! Without water, they just can't possibly breathe air. For this exact reason, Scientists have mentioned that Northern Snakeheads may be able to survive outside of the water for several days if they are in a moist environment (i.e. monsoon season in Asia); however, under the USA's weather conditions, Northern Snakeheads are bound to die in a matter of minutes if exposed to intense sunlight above dry land [49]. Now...there's a big different between a matter of minutes and three days. =)
This is another myth that circulates around the public and the fishing community because of its gross exaggeration by the national media. I can understand how people would be afraid of certain characteristics of the Northern Snakehead because of the lack of scientific evidence in the field nowadays; however, this claim can be debunked with simple fish anatomy and physiology -- knowledge that we already have in our hands!
--
Side note:
The paragraph above is a very good example to support the idea that education and curiosity are both very important factors when it comes to sorting out what is true, what is false, and how much do we take for granted when it comes to a source or piece of information.
I would like to quote something that one of my Math Professors said one day, regarding primary sources (click to be redirected to Wikipedia for its definition):
"Opinion and belief should live in the absence of fact, not in place of it. With so much garbage out there, it's our responsibility to fact check ourselves. Herein lies the problem: we don't usually fact check, and when we do, really getting to the facts is becoming increasingly difficult when everything is packaged in opinion with no reference to a primary source. Advice: if you can't verify something with a primary source, don't consider it fact. You will do everyone a favor."
Even though he's a former Mathematics professor, those words are pretty deep. So, think about it! Did you ever reach primary sources for this Snakehead myth, for example? (i.e. an artifact, document, recording, or other source of information at the time under study)
--
Scientifically speaking, Northern Snakeheads do have the ability to "breathe air;" however, as Dr. Courtenay, Fury, Hill, and Shafland indicate once again: "suggestions that these fish can live without water for up to three days is a gross exaggeration [46]."
I'll go with the "a picture is worth a thousand words" approach here to debunk this myth:
Anatomy and Physiology of the Suprabranchial chamber of a Northern Snakehead. This picture belongs to the Michigan Science Art website.
Do not panic if you did not understand this picture at a first glance. I'll explain:
Different than most types of fish, Northern Snakeheads do "breathe air." This interesting ability is due to the suprabranchial chamber (see it in the picture above), which is actually a series of small spaces that are located in the back portion of their head. On a magnified view -- the pink park on the bottom of the picture (epibranchial respiratory fold), one can see that these spaces are filled with folded tissues with high surface areas. These folded tissues allow the Snakeheads to exchange oxygen directly from air to their blood [47].
--
Side note:
Here's the catch, though: this is science, and not magic. Something extra is needed in other to transfer oxygen from one medium to another (click to be transferred to the definition of medium). For example: we -- human beings -- need our diaphragm in order to breathe and our alveoli in order to exchange carbon dioxide for oxygen.
A picture portraying the process of inhaling (breathing in) and exhaling (breathing out). Notice the difference in the volume of the thoracic cavity. The picture belongs to the Encyclopedia Britannica, Inc.
Not only the diaphragm divides our thoracic cavity (lungs, heart, etc) from our abdominal cavity (stomach, intestines, etc); it allows air to flow in our lungs as it contracts. In other words, the diaphragm plays a fundamental role in human respiration: as it contracts, our thoracic cavity's volume increases, allowing air to flow from outside into our lungs. Once it retracts, our thoracic cavity's volume decreases, and then the air flows from our lungs to the outside. This is basically the concept of inhaling and exhaling that every college student goes through in a Biology class (Human Anatomy and Physiology), and it's inside the lung where we exchange our body's carbon dioxide with fresh oxygen.
--
Snakeheads, however, do not have a diaphragm to help them breathe air. Instead of that, they have the suprabranchial chamber that I described above. Instead of having alveoli to exchange carbon dioxide for oxygen and vice-versa, Snakeheads use water: during each breath, the water in the surface area of the folded tissues in the chamber allows oxygen to be absorbed by the fish, directly into their bloodstream [48]!
Thus, their ability to breath air is very limited. So, even when Northern Snakeheads are completely outside of the water, they still depend on water to breathe! Without water, they just can't possibly breathe air. For this exact reason, Scientists have mentioned that Northern Snakeheads may be able to survive outside of the water for several days if they are in a moist environment (i.e. monsoon season in Asia); however, under the USA's weather conditions, Northern Snakeheads are bound to die in a matter of minutes if exposed to intense sunlight above dry land [49]. Now...there's a big different between a matter of minutes and three days. =)
4. "Northern Snakeheads spread to different regions and states from Crofton Pond, MD"
For some reason, many anglers believe that the whole spread of Northern Snakeheads in the United States of America started at Crofton Pond, MD. In other words, some people believe that all the Northern Snakeheads found around the country nowadays "migrated" from Maryland at a certain point in time. It's true that most of our attention towards the Species started with the Crofton incident (see section one); however, is this migration theory really valid? Were they present at other watersheds prior to this incident?
Myself, I've talked to plenty of local anglers about the spread of Northern Snakeheads in Philadelphia. Some anglers truly believe that the Northern Snakeheads that were first found in the Meadow Lake (FDR Park -- Franklin Delano Roosevelt) came from the Schuylkill River, which came from the Delaware River, etc. However, is there any substantial proof that the migration route that they cited is true? What if it happened the other way around? What if everything started at Meadow Lake for the same reasons as Crofton Pond?
Here is a map of the spread of the Northern Snakeheads in the USA, as for 2013.
In order to debunk this myth, one can use the method of "contradiction" -- the same one that is usually used in Number Theory (Mathematics). First, let's consider only "position." In our case, let's look at the distribution map and assume that all Northern Snakeheads came, indeed, from Maryland (not only the Crofton Pond, but different watersheds in Maryland). For that to be true, all dotted locations on the map should have bodies of water that are interconnected. After all, since we now know that Northern Snakeheads cannot do overland migrations and they cannot breathe outside of the water for a long period of time (in the USA), it would be impossible for them to go from one body of water to another through land.
If we look carefully at the map, there's a heavy concentration of red dots around Maryland, New Jersey, Delaware, and Pennsylvania. Then, there are a couple dots -- 5 precisely -- around New York and Massachusetts. Finally, we have one dot in Illinois, 2 in North Carolina, 1 in Florida, 2 in Arkansas, and 1 in California.
Thus, by simply looking at the map, it's valid to say that not all those watersheds (red dots) are interconnected along the country; therefore, we have a contradiction as to our initial statement that "all bodies of water must be interconnected." So, the initial idea that all Northern Snakeheads came from Maryland is false.
If we had only the cluster of red dots along MD, NY, DE, and PA, then we could possibly assume that the spread happened from a single source. However, the single or double dots on the other states make this concept very doubtful (if not impossible).
We can also take a look at the "time-frame" of the discovery of Northern Snakeheads in some US waters:
Silverwood Lake, California, October - 1997 [50]
Saint Johns River, Florida, 2000 [51]
Newton Pond, Massachusetts, October - 2001 [52]
Crofton Pond, Maryland, May - 2002 [53]
Lake Wylie, North Carolina, July - 2002 [54]
Potomac River, Maryland & Virginia, April -2004 [55]
Meadow Lake, Pennsylvania, July - 2004 [56]
Massey Creek, Virginia, 2005 [57]
Little Hunting Creek, Virginia, 2005 [58]
Anacostia River, Maryland, 2007 [59]
Ditch near Monroe, Arkansas, April - 2008 [60]
Delaware River Tributaries, New Jersey, 2009 [61]
As one can see, a couple Northern Snakeheads were discovered way prior to 2002 (the Crofton incident); therefore, those fish can't possibly be related to Maryland at all.
It's also important to cite that there's a difference between established and non-established populations of Northern Snakeheads in US waters. Basically, established populations mean that they can breed on their own in the wild [62]. As for now, established populations are in Virginia, Maryland, Pennsylvania, New York, and Arkansas. Non-established populations are in California, Florida, Illinois, Massachusetts, Delaware, and North Carolina [63].
Notice that all findings prior to 2002 are non-established populations of Northern Snakeheads. That's exactly why the Crofton incident was such a big deal. As cited before, it was a case of an established population of Northern Snakeheads! This is the reason, perhaps, as to why people believe nowadays that the spread started at that specific location: at a little pond behind a Dunkin Donuts in Crofton.
However, after more studies were performed on the distribution and the growth of the Northern Snakeheads, scientists started to find out that certain established populations of it were in certain watersheds prior to 2002. The Potomac River is a great example [64]. Although there's no substantial evidence, one can also assume that Northern Snakeheads were in Meadow Lake (FDR Park), Philadelphia, way prior to 2004 -- when the first sample was collected.
It's based on these grounds that another hypothesis came up a while ago: Northern Snakeheads did not migrate to other watersheds from Maryland. They were simply introduced to different bodies of water by different people, all along the country.
Since Northern Snakeheads were legally imported and sold as live food fish prior to 2002 [64], anyone could actually purchase some and just release them in their local bodies of water. Also, there's a long story intertwining Northern Snakeheads and aquarium trade [65]. As mentioned before in this post, people could easily release their pets in local waters due to their overgrown sizes. With these two factors in mind, there were plenty of chances for the introduction of Northern Snakeheads in US waters. Thankfully, not every introduced fish was able to breed and have a established population, either because only one sample was released (i.e. a pet), or the few released samples were all of the same gender.
The idea of multiple sources was finally proved once scientists decided to take the DNA of multiple Northern Snakeheads from different locations and see if they were related to each other. In particular, scientists took the DNA of Northern Snakeheads from the Potomac River and compared it to the DNA of Northern Snakeheads from the Crofton Pond. The results were very interesting: 16 samples from the Potomac were tested and 15 out of the 16 were related to each other. On the other hand, none of the 16 samples were related to the Northern Snakeheads from Crofton Pond [66]. In conclusion, the Northern Snakeheads from the Potomac River did not migrate from Crofton, Maryland. The established populations there were probably due to someone releasing them in the Potomac itself.
Therefore, the idea of a single source for all Northern Snakeheads in the United States of America is certainly a myth. There's substantial evidence nowadays that they were released illegally in different states, and unfortunately, some of the released samples were able to breed and establish their own populations.
5. "Northern Snakeheads are on top of the food chain (by themselves)"
In terms of other fishes, adult Northern Snakeheads have no other aquatic predators. Therefore, taking only freshwater in consideration, they are on top of the food chain indeed.
However, the sentence is misleading because people often don't realize that Northern Snakeheads are not the only ones on top of the food chain. According to the standard classification in Biology, the aquatic food chain goes like this:
However, the sentence is misleading because people often don't realize that Northern Snakeheads are not the only ones on top of the food chain. According to the standard classification in Biology, the aquatic food chain goes like this:
Freshwater Food Chain Example -- click on it for magnification. Sorry for the low quality of it! I made it on Paint.
This is the general chain that applies for freshwater. First we have the predators (mostly Game-fish) would be the Bass family (i.e. Striped, Largemouth Smallmouth), the "Esox" family (i.e. Chain Pickerel, Muskellunge, Northern Pike), the Walleye, the Catfish family (i.e. Channel, Flathead, Blue), etc. Then we have the small fishes (mostly bait fish/micro fish): the Sunfish family (i.e. Bluegills, Pumpkinseed, Green, etc.), the Perch family (i.e. White and Yellow), the Shiner family (i.e. Golden, Satinfin, etc.), the Killifish and Mummichogs, etc. And then, finally, we have zooplankton (tiny animal organisms) and phytoplankton (tiny plant-like organisms).
As you can see, the chain pretty much starts with the phytoplankton and ends with the Large Fishes for freshwater. Therefore, scientifically speaking, Northern Snakeheads are in the same category as Largemouth Bass, Northern Pike, Walleyes, Chain Pickerel, Smallmouth Bass, etc. Northern Snakeheads are on top of the freshwater food chain, but they are not alone.
Also, it's worth to mention that this food chain is "size-dependent." For example: just like any other Species of fish, small and juvenile Northern Snakeheads can be a target by other Large Fishes. As a matter of fact, small Northern Snakeheads are yellow/orange in color (see photos below); thus, making them an easy target for other predators. Also, just like other large Species of fish around, Snakeheads will practice cannibalism upon lack of food [67]. Therefore, regardless of their main classification in the food chain, they will eat one another depending on their relative sizes: big Bluegills will eat small Shiners. Northern Pike will eat small Largemouth Bass. Largemouth Bass will eat small Northern Snakeheads, and so on.
Photo of a small Northern Snakehead (~3 inches). Photo by Jimmy Ly.
A school of Northern Snakehead fry. Photo by Jimmy Ly.
--
Side Note:
"Look for the orange basketball."
That's exactly what a local angler told me when I first started to fish for Northern Snakeheads. At the beginning I didn't quite understand it. I mean...what did a Basketball have to do with Snakeheads?
Soon I realized what the angler was referring to: the Juvenile Northern Snakeheads!
During post-spawning season for Northern Snakeheads, one of the main techniques in catching them is "stalking" -- by using a pair of polarized lenses, an angler is able to walk around and locate fish in the water. In this case, all the angler needs to do is to find the "orange basketball." If there's a concentration of juvenile Northern Snakeheads swimming in a circular motion (forming an "orange basketball"), it's very likely that its parents are going to be around!
Usually, there's always at least a female or a male protecting their breed. By casting towards the "orange basketball," there's a high percentage of chance that the parents are going to strike. As a matter of fact, they will strike anything that comes close to their "kids" (see myth number 6 below). Any type of lure that resembles a fish or any other live organism will work! Sometimes, the angler is able to catch the male and the female, one cast after the other!
--
Now...this food chain that I've created on Paint is very limited. When it comes to a larger food chain, then you could have the birds on it, for example. The same birds that predate on Trout will go for Northern Snakeheads, especially since they are easy targets when breathing air on top of the water. Cormorants will definitely eat juvenile Northern Snakeheads. And so on. If the sizes are right, different types of birds will definitely eat them!
Summarizing...Northern Snakeheads are on top of the food chain; however, they are not the only ones! Also, just because they are invasive, it doesn't mean that they are "invincible:" juvenile ones are easy targets for other native larger Species of fish, and even adult Northern Snakeheads can be targeted by certain bird Species.
Now...this food chain that I've created on Paint is very limited. When it comes to a larger food chain, then you could have the birds on it, for example. The same birds that predate on Trout will go for Northern Snakeheads, especially since they are easy targets when breathing air on top of the water. Cormorants will definitely eat juvenile Northern Snakeheads. And so on. If the sizes are right, different types of birds will definitely eat them!
Summarizing...Northern Snakeheads are on top of the food chain; however, they are not the only ones! Also, just because they are invasive, it doesn't mean that they are "invincible:" juvenile ones are easy targets for other native larger Species of fish, and even adult Northern Snakeheads can be targeted by certain bird Species.
6. Northern Snakeheads will bite/attack people and pet-dogs"
7. "Northern Snakeheads go under the mud and hibernate during the winter"
COMING SOON
--- The Known Impact of Northern Snakeheads in our Aquatic Ecosystems Up to Date ---
COMING SOON
--- The Future of Northern Snakeheads: Acceptance or Denial in the Fishing Community? ---
COMING SOON
References:
[1] B. Carolyn, Invaside Snakehead Fish spreads in Philly Waterways (March, 2012)
[2], [4], [6], [7] H. Robert, The Northern Snakehead: An Invasive Fish Species, Review Article (August, 2002)
[3], [19], [21], [34], [49], [50-54], [66], [67] W. R. Jr. Courtenay, J.D. Williams, Snakeheads (Pisces, Channidae) - a Biological Synopsis and Risk Assessment (2004)
[5] M. Hillary, Maryland Suffers Setback in War on Invasive Walking Fish (July 2002)
[8], [9] H. Anita, Snakeheads' Luck Put Pond in the Soup (July 2002)
[10], [11], [30], [32-33], [65] C. Steve, C. Melissa, C. Don, R.C. Walter, C. Jim, E. Ken, G. Jim, H. Richard, K. Cindy, L. Bob, M. Steve, O. John, O. Tom, R. Brian, S. Jon, & S. Julie, National Control and Management Plan for the Northern Snakehead (Channa Argus) (Draft)
[12], [24], [29], [64] C. Patterson, Urban Jungle: The Changing Natural World at our Doorsteps (April 2013)
[13], [17] Unknown, Another Exotic Species Confirmed in PA Waters (July 2004)
[14] L. Chris, "Frankenfish" Invade Philly Waters (March 2012)
[15] D. Mark, Northern Snakehead Invading Delaware River (September 2013)
[16] D. Molly, Voracious "Frankenfish" Spotted in Heinz Wildlife Refuge, Delaware County (March 2012)
[18] D.R. Zach, Snakehead Fish Invade Newton Lake (July 2013)
[20], [22-23], [25], [36], [38], [42], [44], [46] G. Ronnie, Scientists Challenge Snakehead Myths (April 2013)
[26], [47], [48] P.B. Moyle, J. J. Jr. Cech, Fishes - An Introduction to Ichthyology, 5th Edition (2004)
[27-28] N.W.R. Lapointe, J.T. & Thorson, P.L. Angermeier, Seasonal Meso- and Microhabitat Selection by the Northern Snakehead (Channa argus) in the Potomac River System (2010)
[31], [43], [45] T.M. Orrell, L. Weigt, The Northern Snakehead Channa Argus (Anabantomorpha: Channidae), a non-indigenous fish Species in the Potomac River, USA (2005)
[35] R. J. Stuber, G. Gebhart, & O.E. Maughan, Habitat Suitability Index Models: Largemouth Bass (1982)
[37] L. M. Herborg, N.E. Mandrak, B.C. Cudmore, & H.J. MacIsaac, Comparative distribution and invasion risk of Snakehead (Channidae) and Asian Carp (Cyprinidae) Species in North America (2007)
[39] J. Odenkirk, S. Owens, Expansion of a Northern Snakehead Population in the Potomac River System (2007)
[40] J. Love, J.J. Newhard, Will the Expansion of Northern Snakehead Negatively Affect the Fishery for Largemouth Bass in the Potomac River (Chesapeake Bay)? (September 2012)
[41] A. Faulds, Meet the Flathead Catfish: Recently Introduced to the Delaware Watershed (July-August 2002)
[55], [57-63] Fuller, P.F., A.J. Benson, & M.E. Neilson, Northern Snakehead Sightings Distribution (May 2013)
[56] PA Fish and Boat Commission Press, Another Exotic Species Confirmed in PA Waters (July 2004)
[67] Baltimore Sun Associated Press, Potomac Snakeheads not Associated to Others (April 2005)
THIS IS A WORK IN PROGRESS. =)
[2], [4], [6], [7] H. Robert, The Northern Snakehead: An Invasive Fish Species, Review Article (August, 2002)
[3], [19], [21], [34], [49], [50-54], [66], [67] W. R. Jr. Courtenay, J.D. Williams, Snakeheads (Pisces, Channidae) - a Biological Synopsis and Risk Assessment (2004)
[5] M. Hillary, Maryland Suffers Setback in War on Invasive Walking Fish (July 2002)
[8], [9] H. Anita, Snakeheads' Luck Put Pond in the Soup (July 2002)
[10], [11], [30], [32-33], [65] C. Steve, C. Melissa, C. Don, R.C. Walter, C. Jim, E. Ken, G. Jim, H. Richard, K. Cindy, L. Bob, M. Steve, O. John, O. Tom, R. Brian, S. Jon, & S. Julie, National Control and Management Plan for the Northern Snakehead (Channa Argus) (Draft)
[12], [24], [29], [64] C. Patterson, Urban Jungle: The Changing Natural World at our Doorsteps (April 2013)
[13], [17] Unknown, Another Exotic Species Confirmed in PA Waters (July 2004)
[14] L. Chris, "Frankenfish" Invade Philly Waters (March 2012)
[15] D. Mark, Northern Snakehead Invading Delaware River (September 2013)
[16] D. Molly, Voracious "Frankenfish" Spotted in Heinz Wildlife Refuge, Delaware County (March 2012)
[18] D.R. Zach, Snakehead Fish Invade Newton Lake (July 2013)
[20], [22-23], [25], [36], [38], [42], [44], [46] G. Ronnie, Scientists Challenge Snakehead Myths (April 2013)
[26], [47], [48] P.B. Moyle, J. J. Jr. Cech, Fishes - An Introduction to Ichthyology, 5th Edition (2004)
[27-28] N.W.R. Lapointe, J.T. & Thorson, P.L. Angermeier, Seasonal Meso- and Microhabitat Selection by the Northern Snakehead (Channa argus) in the Potomac River System (2010)
[31], [43], [45] T.M. Orrell, L. Weigt, The Northern Snakehead Channa Argus (Anabantomorpha: Channidae), a non-indigenous fish Species in the Potomac River, USA (2005)
[35] R. J. Stuber, G. Gebhart, & O.E. Maughan, Habitat Suitability Index Models: Largemouth Bass (1982)
[37] L. M. Herborg, N.E. Mandrak, B.C. Cudmore, & H.J. MacIsaac, Comparative distribution and invasion risk of Snakehead (Channidae) and Asian Carp (Cyprinidae) Species in North America (2007)
[39] J. Odenkirk, S. Owens, Expansion of a Northern Snakehead Population in the Potomac River System (2007)
[40] J. Love, J.J. Newhard, Will the Expansion of Northern Snakehead Negatively Affect the Fishery for Largemouth Bass in the Potomac River (Chesapeake Bay)? (September 2012)
[41] A. Faulds, Meet the Flathead Catfish: Recently Introduced to the Delaware Watershed (July-August 2002)
[55], [57-63] Fuller, P.F., A.J. Benson, & M.E. Neilson, Northern Snakehead Sightings Distribution (May 2013)
[56] PA Fish and Boat Commission Press, Another Exotic Species Confirmed in PA Waters (July 2004)
[67] Baltimore Sun Associated Press, Potomac Snakeheads not Associated to Others (April 2005)
THIS IS A WORK IN PROGRESS. =)