How to deflate your fish   

By Raymond Wilson, PHD, Univ. South Fla. 

You've hauled the poor fish to the surface. His eyes bulge. His stomach sticks out of his mouth.

How can you possibly put him back in the water, with or without a tag? You can't unless you vent his swim bladder gases.

The swim bladder is a closed internal organ filled with gases, mostly oxygen an nitrogen. It sits in the abdominal cavity along the backbone beneath the first dorsal fin.

Except for sharks and rays, most marine fishes have a well-developed swim bladder. They use it to remain buoyant at whatever depth they normally live.

When fish are at rest, the pressure of the gases in the swim bladder equals the pressure exerted by the surrounding water. The gases are compressed and the swim bladder occupies a relatively small space.

If you bring the fish rapidly to the surface, the outside pressure lessens and the gases in the swim bladder expand in direct proportion.

Say you catch the fish at a depth of thirty-three feet. By the time you bring him to the surface, the gases in his swim bladder will occupy twice their original volume.

Swim bladders can stretch only so far before they burst. When they do, the gases escape into the fish's abdomen, where they continue to expand. This puts pressure on the stomach, the intestines, and other internal organs.

To return the fish safely, you must vent those gases. And you must do it without further injuring the fish.

What's the best way to do this?

Don't try to force the stomach or other organs back into the body cavity. And don' t vent the gases by puncturing the protruding stomach or going through the anus. The fish might swim away. He probably won't survive.

Most fish are hardy beasts and can survive the trauma of a ruptured swim bladder. If properly deflated and returned, many will survive, grow and reproduce. **

Click here for more details and photos showing how to vent bottom fish.