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surface from deep water. Several studies, including one from South Dakota, indicate that barotrauma most likely occurs when fish are caught from depths of 30 feet or more. Potential symptoms of barotrauma in fish include the stomach protruding out of the mouth, a ruptured swim bladder, gas bubbles within the blood or organs, hemorrhaging of internal organs, bulging eyes and loss of equilibrium. Fish experiencing a loss of equilibrium often cannot swim back to the depth where they were caught, making them vulnerable to delayed mortality due to exposure, predation, and stress from surface temperatures. Fish experiencing moderate-to-severe barotrauma often experience mortality when released.
Some fish species are less susceptible to barotrauma, but they can still experience it. These species have an open connection between the swim bladder and their gut, allowing air to pass directly out as they are reeled up. These fish are termed physostomous and include northern pike, trout, and salmon.
Species with a closed connection between the swim bladder and the gut are more susceptible to barotrauma. These fish are referred to as physoclistous and include walleyes, yellow perch, smallmouth bass and largemouth bass. In physoclistous fish, the swim bladder is regulated by diffusing gases from the blood, a process much slower than simply passing gas( i. e., burping), which physostomous fish can do. This closed connection prevents rapid changes in the amount of gas in the swim bladder, making these fish more prone to barotrauma.
Biologists and anglers have proposed various methods to relieve the symptoms of barotrauma in an attempt to improve their survival when released. Some of these include reeling the fish in slowly, reeling the fish in fast, removing air from the mouth cavity before releasing, venting, attaching the fish to a weighted descending device to return it quickly to the depth where caught, and attaching weighted metal clamps to the fins of fish held in livewells to reduce their buoyancy and help with equilibrium issues.
Venting, also known as fizzing,
is a technique used to alleviate barotrauma in fish by releasing excess gas from their swim bladder. This should only be done when a deep-water caught fish cannot maintain its orientation. This process involves inserting a hollow needle, typically at least 16-gauge and 1.5 inches long, through the fish ' s side into the swim bladder. The needle is inserted at a 30- to 45-degree angle behind the tip of the pectoral fin( side fin). The fish is then submerged underwater, and the needle is raised to a 60- to 90-degree angle until air bubbles are seen. After a few seconds, the needle is removed, and the fish is released. Due to the risk of damaging internal organs, venting should only be completed by individuals trained in the proper technique.( Readers should note that venting fish is illegal in Minnesota.)
A 2016 study in Saskatchewan, Canada, evaluated barotrauma relief treatments of venting, descending device and fin weighting on walleyes caught during September. One component of the study focused on the short-term health of walleyes with barotrauma after treating them with fin weighting or venting. Fin weighting was found to immediately improve walleye condition by making them upright, but only 53 percent
of these fish recovered adequately to be released. Venting appeared to be better than fin weighting, as 73 percent of the vented walleyes were able to be released.
The other component of the study used acoustic telemetry to monitor walleye movements after they were vented and released or released with a descending device. Walleyes released via a descending device had post-release movements, occupied depths, and use areas similar to the control walleyes( no barotrauma). Vented walleyes made shorter post-release movements, used shallower water and occupied smaller areas than those released with a descending device or the control walleyes.
The study concluded that without some intervention, a large portion of walleyes exhibiting moderate-to-severe barotrauma will likely die, and it; s best to try to relieve the symptoms. The use of a descending devise was recommended over venting as a more effective treatment to increase the survival of walleyes experiencing barotrauma. Unfortunately, the study only addressed the shortterm( 7 days) behavior and mortality, and further research is needed, as it’ s unknown what the long-term impact is on these fish. The authors emphasized that the
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