CO2 Fish Barriers

Asian carp are here in the US to stay. This group of fishes are often called Bigheaded carps, and typically includes silver carp, bighead carp, grass carp, and black carp. Each species was brought to the US from Asia for different reasons—for example, grass carp were introduced for weed control as they eat vegetation.  Each species was also likely introduced multiple times to natural habitats, and today these carps can be found across much of North America. You may recognize silver carp, which are well known for their jumping behavior in the presence of boats.

Jumping carp (Source:

Jumping carp. (Source:

From multiple locations, Asian carp have been expanding their range in North America. The current concern is that they will make their way into the Great Lakes, where they will have many negative impacts on the ecosystems and fisheries of the Great Lakes. (But to be clear, the Great Lakes are home to many, many introduced species that have rendered the current Great Lakes into systems that already might not represent their former pristine selves.) Asian carp are well-established in the Illinois River, and migrating north through the Chicago Sanitary and Ship Canal—the connection between the Illinois and Mississippi Rivers and the Great Lakes—would mean their introduction into the Great Lakes.

Currently, an electric barrier exists in the Chicago Sanitary and Ship Canal, and an electric barrier is exactly what it sounds like—an electric field present in the canal’s water that acts as a strong deterrent against fish passage. Basically, fish have no incentive to swim through electrified water once they feel the shock. So far, the electric barrier seems to be working well, but no barrier is 100% effective. Electricity may fail, eggs or larvae may pass, or many other things may occur to permit fish passage. A redundant barrier is being sought.

Schematic of electric barrier in Chicago Sanitary and Ship Canal (Source:

Schematic of electric barrier in Chicago Sanitary and Ship Canal. (Source:

Recently, there has been a lot of activity behind the idea of a using carbon dioxide as a redundant barrier to the electric barrier. Fish are generally repelled from CO2, which in high concentrations can sedate or even anesthetize fish. But weaker concentrations of CO2 in water are showing promise to repel fish, as if there were a foul smell in the air that would cause you to turn around and not want to approach.

The idea behind a CO2 barrier is not create a ‘bubble curtain’ but to actually infuse the water with high concentrations of dissolved CO2. Although river locations are still under consideration (you can’t infuse entire rivers), this infusion would likely take place in a small portion of the river through which everything must pass—like a shipping lock! Shipping locks could be pumped full of CO2, and then opened, as part of their regularly scheduled use. The plume of CO2-rich water would then dissipate downstream, pushing Asian carp back and ultimately discouraging them from any further migration.

30,000 gallon high-velocity flume operated by the US Army Corps of Engineers (Source: Steve Midway)

30,000 gallon high-velocity flume operated by the US Army Corps of Engineers. This facility can be operated with CO2-infused water to simulate a river environment. (Source: Steve Midway)

Of course, CO2 impacts all fishes, and in fact other less mobile organisms, too, such as mussels and other aquatic invertebrates. So while it might be clear that CO2 use to deter Asian carp is a good thing, unintended impacts need to also be assessed. It could be that the CO2 doesn’t stick around in the water long enough to negatively impact other biota, or that other mechanisms exist to minimize CO2 on non-Asian carps species. CO2 impacts on fish is a very new field of study—namely because the need to create defenses against introduced species often come with little warning. However, much of the early work looking at CO2 use as a barrier suggests very good potential.

What do you think about pumping huge volumes of CO2 into rivers to contain invasive species? Leave us your thoughts in a comment. 

Steve Midway


7 responses to “CO2 Fish Barriers

  1. Has any one looked at what the possible repructions of CO2 lowering the pH and acidifying the water? Will the effect be diluted or just pushed down stream?

    • That’s a great observation, and based on this question and a few others, I’m going to have a follow up post in a few weeks that answer this and other concerns people have about pumping CO2 into a river.

  2. Steve, I think you touched on the critical issue in your third paragraph; egg and larval transport downstream. Electricity and CO2 barriers may impede adult and, to some extent larval emigration, however egg transport will still occur.

    • Fortunately, much of the prevention is geared toward keeping things from moving upstream. However, flowing waters should not always be viewed as uni-directional as things (from elements to organisms) move up and downstream.

  3. I did my masters thesis on the effects of CO2 on the swimming ability and respiration rates of larval red drum. Although the chemistry in saltwater is slightly different, the effects on fish are essentially the same. Increased CO2 has been shown to increase otolith size which has negative effects on auditory detection. Data show that with this increase, larvae are able to detect lower sound frequencies which have negative repercussions in their ability to find natal settlement sites based on auditory detection. CO2 has also been shown to affect, homing and navigation ability, predator/prey detection, olfactory and visual acuity, habitat selection, mate selection, and a range of other physiological and ecologically important processes. My own research showed that in extreme cases it affects larval swimming ability and respiration rates. The idea of a CO2 barrier might seem like an easy, sexy idea, but I’m afraid in reality the side effects might be ecologically devastating. I wrote a post on my own blog reviewing some of these effects in CO2 environments. It can be found here:

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