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Releasing Bottom Fish and Venting


The release techniques for bottom fish are similar to those for other fish, however bottom fish taken from the deep fill with gas and may need venting to increase their survival rate when released.


Many marine reef fish have a gas-filled swimbladder that controls buoyancy to allow the fish to maintain a certain depth in the water column.


Reef fish taken from depths of 50 feet or more may undergo expansion of the gases in the swim bladder as they are brought quickly to the surface on hook and line. Swimbladders can expand only so far before they burst. When the swimbladder bursts, the gases escape into the fish’s body cavity, where they can continue to expand.

The pressure exerted by the gases on the fish's internal organs is considerable, and can result in serious injury to the fish. The pressure may often be sufficient to push the stomach out of the mouth, and the intestines out of the anus.


If the fish is released in this buoyant condition, the fish may float away and die from exposure to the elements, or become an easy target for predators.


When retrieving a reef fish, carefully assess its condition.  If the fish is bloated and floats (is unable to control its buoyancy) or if the fish’s stomach is distended from the mouth, the fish requires venting.  If the fish appears normal, not bloated, and appears like it would be able to swim down to the depth where it lives, venting is not necessary.      


Venting tools


A venting tool is a device to deflate the expanded air from the swimbladder of a fish retrieved from depth, with minimum damage.  A venting tool must be a sharpened, hollow instrument, such as a hypodermic syringe with the plunger removed, or a 16–gauge needle fixed to a hollow wooden dowel.  A knife, ice-pick, larger needles or other penetrating devices are strongly discouraged.


To properly vent a fish, the tool is inserted into the fish at a 45–degree angle approximately1 to 2 inches (2.54 to 5.08 cm) behind the base of the pectoral fin. The tool should be inserted just deep enough to release the gases to avoid damage to internal organs.


At least one venting tool is required and must be used when needed to deflate the swimbladders of Gulf of Mexico reef fish that will be released.  


Here are some resources:


To view a video on how to vent fish with minimum damage, go to:


Great illustrative photos and info on how to vent from Florida Sea Grant :