Barotrauma refers to physical damage to body tissues caused by rapid decompression which may be brought about by several scenarios that lead to rapid changes in air or water pressure such as altitude or water depth changes.
Barotrauma related injury occurs through two pathways governed by either Boyle’s or Henry’s gas laws. Boyle’s law – related injuries are due to the expansion of free gas in body cavities and Henry’s law -related injuries are caused by dissolved gases escaping solution to form bubbles in body tissues and fluid vessels.
In fish, barotrauma is due initially to the overstretching of organs that contain air filled cavities (Boyle’s law) such as the gas bladder and digestive tract. Overexpansion of the gas bladder can impair mobility, buoyancy control and cause disorientation.
Even mild barotrauma may cause fish to be stranded at the surface of the water where they may be susceptible to overheating (summer), freezing (winter) and to boat and bird strikes. Further overexpansion of free gas can lead to rupture of these organs and escaping gases can cause severe and unpredictable damage to other internal organs.
Barotrauma is further complicated by the formation of gas bubbles (emboli) in blood and other fluid vessels or in muscle, connective and organ tissues (emphysema) (Henry’s law). Henry’s law – related injuries have several consequences including cardiovascular and organ failure and sensory impairment. Individual or combined injuries from barotrauma may result in impairment of a fish’s normal behavior such as escaping from predators or finding enough forage to survive.
The occurrence of barotrauma in fish is well established for marine fish angled at extreme depths as well as in fish passing through hydroelectric turbines. The impacts of rapid decompression have also been measured in relatively shallow-dwelling freshwater fish species such as bluegills, black crappies, northern pike, white sturgeon, and walleye.
Barotrauma is relevant to freshwater anglers targeting fish in both deep waters and relatively shallow waters (at or greater than ~25-30 ft). At the depth of ~30 ft, gases are under an additional atmosphere of pressure and their volume is ½ of what it would be at the surface. Fish brought to the surface from these depths have been documented to experience moderate or even severe barotrauma.
- What does disease caused by Barotrauma look like
The most obvious signs of barotrauma in fish are behavioral changes such as disorientation, difficulty maintaining buoyancy, and an inability to keep upright. Fish experiencing barotrauma may show external disease signs such bulging eyes, protrusion of the stomach into the mouth, bleeding form the gills, or the appearance of gas bubbles in the eyes and face. However, a cursory external exam cannot determine if a fish is experiencing barotrauma since internal damage may occur without obvious external signs.
- Fish species affected
Fish differ in their susceptibility to barotrauma based on their physiology and behavior. One of the major determinants of a fish’s susceptibility to barotrauma relates to the morphology of their gas bladder. This organ allows fish to control their buoyancy by both inflating the organ using gases from the blood stream as well as by contracting a layer of muscle surrounding the gas bladder. Physostomous fish like lake trout, muskellunge and sturgeon can expel gas from their air bladder into their digestive tract allowing them to “burp” gas and avoid some of the effects of barotrauma. Physoclistous fish such as black crappie, smallmouth bass and walleye lack the ability to expel gas through their air bladder and are more susceptible to some barotrauma effects. In physostomes, delicate organs responsible for adding or removing gases from the gas bladder (gas gland and ovale) can also be damaged and result in more severe buoyancy control impairment.
- Are fish with barotrauma safe to eat?
Fish experiencing barotrauma are safe to eat. It is common to encounter fish with barotrauma while angling especially in scenarios where fish are expected to be targeted at depths at or greater than 25-30ft. For this reason, it is advisable to keep your catch and stop when you reach your limit when you are angling at these depths.
- How can I prevent impacts of barotrauma
As an angler, you can prevent impacts of barotrauma by choosing to fish in shallow water (less than 30 ft) especially when targeting sensitive species like walleye, and panfish for catch and release angling. It is recommended that anglers plan and prepare to keep their catch for consumption when targeting sensitive species in deeper waters.
Knowing the signs of barotrauma helps anglers make informed decisions about whether to keep a fish that they have caught. If a fish appears to be suffering from severe signs of barotrauma it preferable to keep that fish instead of releasing it. Make sure to consult the fishing regulations (Fishing regulations | Minnesota DNR (state.mn.us))
It has become a common practice to attempt to remedy barotrauma in marine fish caught at extreme depths by fizzing, venting, or puncturing the gas bladder of a fish to release trapped air so that the fish can return to depth rather than being stranded at the surface. However, the benefits of these remedies in fish that inhabit shallow lakes is questionable and is illegal in Minnesota. If you believe a fish is experiencing barotrauma, choose to harvest the fish, or release the fish as quickly as possible.