What is barotrauma? Simply stated barotrauma is “injury caused to the body by changing air or water pressure.” In humans we know this as “The Bends”- a dangerous condition that divers experience when they come up too fast from deep water. Believe it or not, something similar happens in fish.
For example: When an angler angles walleye at the bottom of the lake, those walleye are experiencing a certain amount of pressure (air & water). When the angler yanks them up to the surface, that pressure is drastically reduced. This means that their gas filled cavities rapidly expand. This is particularly a problem for fish due to the presence of their swim bladder; The swim bladder is a balloon like organ that fish use to regulate buoyancy. To remain at a certain depth fish must balance the force of gravity with their own force of buoyancy. They do this thanks to the swim bladder, which expands and compresses with changes in pressure. For an schematic example of how the swim bladder works check out the quick video I posted below. Unfortunately when we pull these fish up from deep depths they become positively buoyant and are unable to regulate that swim bladder effectively. Barotrauma is most commonly known for its prevalence in deep sea fish (e.g. rock fish), however it is also a problem for a freshwater fishes.
Symptoms of barotrauma vary depending on the species
Physoclistous species are fish with swim bladders that are NOT connected to their mouth. These include Yellow Perch and Walleye. The only way these fish can remove gas in their swim bladder is by slowly diffusing it out of the swim bladder through the blood stream. When these species are brought up from deep water they are often seen with a protruding stomach and bulging eyes.
Physostomous species, such as carp, trout, pike and salmon are those which have a direct connection between their swim bladder and mouth. This means these species can remove air from the swim bladder more easily. For example, you may have heard or seen a lake trout burp air out when brought to the surface.
There are many other NON-VISIBLE symptoms and injuries of barotrauma (e.g., hemorrhaging). If you are fishing in deep water (>25 ft), the fish you catch are likely experiencing some degree of barotrauma which may reduce their ability to submerge and survive after release.
So what does barotrauma mean for catch and release?
Unfortunately, the chances of a fish with extreme barotrauma swimming away and surviving is low. Fish with barotrauma typically remain belly up on the surface. Therefore, if you are looking to harvest fish, these fish would be good candidates to keep and count towards your daily limit. Importantly, the impacts of barotrauma on many freshwater species are not well understood. It is likely that some species are able to cope with barotrauma better than others.
There are some options for ‘relieving’ barotrauma
The most well-known technique is called venting or “fizzing.” This is the act of puncturing the swim bladder with a needle, in hopes of deflating it so the fish is no longer positively buoyant. However, there are a number of problems with fizzing which makes it a controversial approach. Most obvious, venting causes a new wound to the fish. This wound is primarily in the swim bladder; an organ that the fish needs in the future to regulate its buoyancy. For many species it is unknown whether and how long it takes for this swim bladder to heal and function normally. Venting can also puncture other organs if the venter has not had extensive training. Venting is sometimes seen as an “out of sight out of mind” approach i.e., it allows you to sink your fish, but we don’t know what happens afterwards. In light of these controversies, many agencies discourage venting.
Non-invasive methods of relieving barotrauma include descending devices. Descending devices work by sending your fish back down to capture depth, and in the process recompressing the gases in the swim bladder and body. If you google “descending devices” you will see a variety of options and videos showing how these devices work. I’ve attached one of the “EcoLeeser” below. Although more literature is needed to see whether these devices work well for freshwater species, there is evidence that this method promotes survival in some marine species. Weighted cages work in a similar way in that you send fish down in an inverted cage and then pull the cage up once you reach capture depth; at this point the bloating in the fish is suppressed and the fish is able to swim and stay submerged (rather than floating up). If you are interested in purchasing a descending device I suggest the Ecoleeser.
What is the best way to deal with Barotrauma? The answer is to move in shallower! If you are fishing at 30ft or deeper there is a good chance these fish will experience barotrauma if angled. Carrying a descending device is not a ‘pass’ to fish in deep water, barotrauma should be avoided at all costs. A responsible angler should do their best to avoid causing barotrauma and should be prepared to deal with it if encountered.