Fish have swim bladders that help them to maintain neutral buoyancy in the water.

Gas is added or removed from the bladder as the fish changes depth. There are two types of swim bladders — physostomous and physoclistic.

The physostomous swim bladder opens directly to the water through the fish’s mouth using a muscular valve to regulate the flow of gas. Most of these fish gulp air from the surface as well as use gas from their gills.

The physoclistic bladder is closed off and can only add or vent gas through the blood via the gills. This does not happen quickly. For species that occupy shallow riffles or live in the mud an air bladder has no advantage.

For these fish, the swim bladder has been lost through the evolutionary process and allows these species to remain on the bottom. Fish without air bladders include darters, dace and the Mottled Sculpin.

Reef fish have a closed swim bladder and it expands rapidly as the fish is reeled in (about 25 percent for each 30 feet of depth). So, if the fish is brought up quickly from deep water it can’t equalize the bladder.

If this fish is released it will be unable to descend until the bladder has been able to vent the excess gas through the blood and gills into the water. During this time the fish is venerable to predation.

In order to allow fish a better chance for survival it is possible for an angler to puncture the air bladder allowing the excess gas to escape. Small fish can be released when pulled up from 30 to 40 feet of water without puncturing the air bladder and with no ill effects.

Often when pulled up from depths greater than 30 feet the result is an excessively inflated air bladder, maybe a swollen abdomen or the air bladder may force the gut lining to protrude out of the mouth.

Anglers shouldn’t attempt to deflate the bladder by piercing the gut lining sticking out of the fish’s mouth. A tear in the gut wall will allow water to get into the body cavity of the fish. This would most likely result in death. Bladder deflation can be done with a sharpened basketball inflator needle or a large gauge hypodermic needle.

These are much better than wire or knife and are easy to obtain. They allow the angler to hear the hiss of escaping air when venting is done correctly.

In red snapper the needle should be at a 45 degree angle and penetrate at a point two thirds of the way back along the pectoral fin. Hissing of escaping air will tell you that you have done it right.

Don’t enter too high up on the body or you will hit the kidney. If you can, keep the fish in a bait tank for a bit until it balances in the water. The small hole made by your tool should readily heal.

In the past, fish swim bladders were used to make a transparent, colorless, water-soluble fish glue called isinglass.

Isinglass was originally made from the air bladders of the Russian beluga sturgeon (Acipenser huso) found in the fresh waters of the Caspian and Black seas.

After restrictions were placed on Russian exports of beluga products in 1939, other fish air bladders were used and isinglass became a generic term for glue derived from the swim bladder of fish, e.g., North American isinglass is made from hake or cod.

To prepare isinglass, the air bladders are removed from the fish, cleaned and air-dried. The dried bladder is cut into thin translucent strips. These strips, which are nearly 80 percent collagen, are dissolved in hot water then diluted and cooled into flat disks.

This very strong, water-soluble adhesive can be used in low concentrations. Isinglass is brittle at a relative humidity below 50 percent and is degraded by UV light. Isinglass is used as a clarifying agent in the beer and wine production, handmade paper, and inks, some paints and anywhere gelatin is used (jelly).

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Dr. “Skip” Lazauski can be seen on his television show “Eco-Bites”, which airs on Mediacom’s channel 14 and Smartel’s channel 4. To reach Dr. Lazauski for questions and comments, send e-mail to IchiOrca@yahoo.com. For more information, see his Web site, www.drskiponline.com.