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Let Em Down Easy: Returning a Fish to Deep Water

Photo by Jeff Gunderson

It's called the ideal gas law: when an air bubble ascends the water column, the decreasing water pressure allows the bubble to grow larger and larger until it reaches the surface. This law of physics is simple enough to be on a 5th grade science test and real enough to affect divers and the fishing world.

Deepwater fishermen both on the coasts and on the Great Lakes might not rattle off the ideal gas law but they are familiar with barotrauma, an affliction in which a fish's swim bladder balloons as the animal is reeled up through the water column. To better understand this, think back to that rising bubble. A swim bladder, a gas-filled organ that allows a fish to travel vertically in the water column by inflating or deflating, is much like that bubble. If a fish has a normal-sized swim bladder while it is swimming 60 feet below the surface, its swim bladder could double, even triple, as a fisherman gives it a quick trip to the surface.

A ballooning swim bladder is a non-issue if the fish will be kept. If it's a catch-and-release kind of fish, however, its life is in jeopardy. With the equivalent of a beach ball in its gut the fish can't swim back down. As it flops at the surface it is fair game for circling gulls.

"There are two types of swim bladders," said Jeff Gunderson, Minnesota Sea Grant's director and fishery specialist. "Some fish have the type of swim bladder that's connected to the gut. They can burp gas to relieve pressure. Other fish can't burp because their swim bladders don't have this connection."

Fish that can burp gas out of their swim bladder include trout and salmon. Fish that lack this ability include walleye and yellow perch. Even though trout have the capability to expel gas, Gunderson explains that a lake trout pulled from deep water might not be able to descend because of barotrauma. So what is a guy or gal with a ballooning fish to do?

The first thing is to understand the signs of a fish struggling with barotrauma, or "pressure" trauma. The physical signs of barotrauma are:

  • Bloated abdominal area,
  • Bulging eyes,
  • Balloon-like tissue protruding from the mouth or other areas of the body (sometimes).

Several techniques have been developed to combat barotrauma. One way to address the problem is "venting," or "fizzing." In this method, fishermen puncture the swim bladder of the fish with a hollow needle to release the excessive air. While venting does help the fish return to deeper water, it can seriously injure other organs during the puncture, eventually leading to death.

Sometimes lake trout can be gently squeezed to help force gas out of the swim bladder, but a better way is to use a descending device an inverted barbless hook with a weight. With this device, secure the weighted hook in the lip, allow the weighted hook to carry the fish to the desired depth, and release the fish with a sharp tug on the line.

"This is an inexpensive, quick, and effective way to release a variety of fish that experience barotrauma," said Gunderson.

Fish suffering from barotrauma can survive if released properly and within two minutes of surfacing. According to a Sea Grant study led by Cal State Long Beach researchers, 83 percent of rockfish caught between depths of 217 and 350 feet survived when dealt with in this way, some even still living 1.5 years after the study commenced.

"There are a variety of new and innovative technologies for releasing fish back into deep water but the low-tech options work quite well," said Florida Sea Grant extension agent John Stevely. Stevely works closely with recreational and commercial fishermen in Florida. "You don't have to send the fish all the way to the bottom," he said. "Drop them down 15 feet and that sets them on their way." He suggests that anglers might be fascinated by the video of a rockfish surviving barotrauma on http://catchandrelease.org, a website crafted by Florida Sea Grant, Florida Fish and Wildlife Conservation Commission, and NOAA Fisheries to share proven catch-and-release techniques.

In the end, if faced with the choice to help the poor fellas descend, do the right thing: let 'em down easy.

A "Do-It-Yourself" Project: Make Your Own Fish Descender

For a few bucks, you might save a life.

Fish Descender


  • Old reel on stiff ice fishing rod

  • Weights (8 ounces weight per pound of fish)

  • Large snap swivels

  • Single hook

  • Pliers


  1. The rounded bend of a single hook fits a fish jaw well. Blunt its point and pinch the barb down.

  2. Tie the hook (or you might want to tie in several for different sized fish) into the line about 12 inches from the end. Tie knots at the eye and bend of the hook with the hook pointing down.

  3. Tie the snap swivel to the end of the line.

  4. Load the line on the old fishing rod and reel.

  5. Add weights to the swivel.

Using Your Fish Descender

  1. Fit the hook over the jaw of the fish

  2. Release the fish, letting the weight pull the fish to at least 15 feet deep or to the depth in which the fish was caught. (The change in water pressure will recompress the fish.)

  3. Give a tug to pop the hook free.

By Russell Habermann
May 2013

Return to May 2013 Seiche

This page last modified on March 01, 2018     © 1996 – 2019 Regents of the University of Minnesota     The University of Minnesota is an equal opportunity educator and employer.
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