Barotrauma, a pressure-related injury, poses a significant threat to the survival of fish caught and released from deep water. This condition occurs when a fish is rapidly brought to the surface, causing an abrupt and severe change in ambient pressure. The result is a cascade of internal injuries that frequently prove fatal, either immediately or through delayed mortality. Barotrauma kills fish primarily by preventing them from swimming back to deeper water. The inability to submerge leaves them vulnerable to predation, boat strikes, and physiological stress from surface conditions.
How Pressure Changes Affect Fish Anatomy
The mechanism behind barotrauma is governed by Boyle’s Law, which states that the volume of a gas is inversely proportional to the pressure exerted on it. As a fish is reeled up from depth, the decreasing water pressure causes the gas within the swim bladder to expand significantly. The swim bladder normally regulates buoyancy, but during rapid ascent, it acts like an over-inflated balloon. This expansion leads to severe physical trauma, displacing or rupturing nearby organs and causing internal hemorrhaging. The forceful expansion can also push the fish’s stomach out through its mouth or anus, a visible sign of internal damage. Fish species that cannot quickly vent this excess gas, such as many bass and snapper, are particularly susceptible to these injuries.
Recognizing the Symptoms of Barotrauma
Barotrauma produces distinct, observable signs of pressure-related injury. One common external symptom is exophthalmia, or the noticeable bulging and distension of the eyes. Anglers may also observe the fish’s stomach or esophagus protruding out of its mouth. The fish’s abdomen may appear bloated and firm due to the pressurized gas inside the body cavity. A major functional symptom is the fish’s inability to swim back down after release, often floating listlessly or on its side at the water’s surface.
Strategies for Injury Mitigation
The most effective way to increase post-release survival is through intervention to relieve excess gas or return the fish to depth. Mitigation is important when catching fish from depths greater than 30 feet, and especially beyond 50 to 65 feet, where the pressure change is substantial. The two primary methods are venting and the use of descending devices.
Venting
Venting involves using a hollow needle or specialized tool to puncture the swim bladder and release the trapped gas, allowing the fish to regain buoyancy control. Proper technique requires inserting the needle behind the pectoral fin, angled slightly toward the head, to reach the swim bladder without damaging other organs. However, venting carries risks, as improper technique can cause further injury or introduce infection, which may lead to delayed mortality.
Descending Devices
Descending devices, also known as recompression tools, are often the preferred method for mitigation. These weighted devices, which may use a lip clamp or inverted hook, rapidly lower the fish back to its capture depth. As the fish descends, the increasing water pressure naturally compresses the swim bladder gas, allowing the organ to return to its normal size. These devices are considered non-invasive and generally safer than venting, reducing the risk of secondary infection and being easier to use correctly. They are designed to release the fish automatically at a pre-set depth or upon reaching the bottom, allowing the fish to swim away under proper pressure conditions. Having both a descending device and a venting tool available is recommended, as certain situations may favor the speed of venting over the retrieval time of a descending device.