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.
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 . 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.
(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.
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 , 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) . 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 ; however, the Northern Snakehead and the Bullseye Snakehead have been proven to not be able to do so .
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) .
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 . 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 .
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 , . 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) .
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) .
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) .
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 . 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 . 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  (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 . 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 ".
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 . 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 .
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!
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 . 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.
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 .
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 .
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! ”
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 .
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 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!
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 ."
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 .
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 !
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 . Now...there's a big different between a matter of minutes and three days. =)
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:
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.
, , ,  H. Robert, The Northern Snakehead: An Invasive Fish Species, Review Article (August, 2002)
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, , ,  C. Patterson, Urban Jungle: The Changing Natural World at our Doorsteps (April 2013)
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THIS IS A WORK IN PROGRESS. =)