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Releasing Reef Fish with Swim Bladder Over-Expansion

Many marine reef fish have gas filled organs called swim bladders. These organs control buoyancy and allow the fish to maintain a certain depth in the water column.

bladder 1

The gas in the swim bladder can over-expand when these reef fish are brought quickly to the surface by hook and line. This can result in serious injuries to the fish and if released in this buoyant condition, it may float away and die. This defeats the purpose of fishery management laws such as minimum size restrictions and daily bag limits.

Swim bladder over-expansion injuries can include Averted stomachs or intestines, as shown below, and may look worse than they really are.

bladder2

These injuries can be treated by venting the gas from the fish's gut cavity. Venting reduces buoyancy and allows the fish to descend, thus giving it a better chance for survival.

VENTING METHODS FOR REEF FISH

Quickly determine if the fish needs to be vented before release. If the fish's stomach is Averted, or the fish is floating on its side and unable to swim down then vent the fish's gut cavity.   Hold the fish gently but firmly on its side and insert the venting tool underneath a scale an inch or two behind the base of the pectoral fin. Only penetrate far enough into the gut cavity for gas to vent and for the gut cavity and averted stomach to noticeably deflate.

bladder3

Return the fish to the water and revive in an upright position until the fish swims away and descends. Do not attempt to push the deflated stomach back down the fish's throat.

bladder4

NOTES ON VENTING

When the fish is brought to the surface closely observe its condition. If the fish is very tired and floats on its side, or if the stomach is distended from the mouth, the fish should be vented. If, when at the surface, the fish is still in an upright position and strongly fighting downward, it may not have to be vented. If possible, hold the fish in the water in an upright position near the boat to check if it can swim down on its own. Then determine if venting is necessary or not. Practice and experience over time will improve your ability to quickly judge the condition of a fish.

VENTING TOOLS

A hollow, sharpened, stainless steel veterinarian's cannula mounted on a wooden handle is the best tool for venting reef fish. The tool should be cleaned between uses and kept in a safe and accessible place.
Fishing Laws are designed to maintain a spawning stock that will ensure the future of a fish species. Compliance with fishing laws is essential for sustaining U.S. sport and commercial fisheries. When compliance means releasing a fish, follow these guidelines to improve its survival.
  • Have a plan for releasing a fish before bringing it in.
  • Avoid using gaffs and landing nets if possible.
  • Handle the fish in the water if possible.
  • Handle with wet hands or a wet towel being careful to avoid the gills and eyes.
  • Back hooks out using pliers or cut the leader as close to the hook as possible on throat-hooked fish.
  • Time is crucial in keeping a release alive.
  • Work quickly and in concert with others on board for quick releases.

  • Revive an exhausted fish in the water with a gentle back and forth swimming motion.

Courtesy of the Florida Sea Grant College Program, University of Florida. This work is a result of research sponsored by NOAA, Office of Sea Grant, Department of Commerce, under Grant Number NA36RG-0070.

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