Fish have swim bladders to help them maintain neutral buoyancy in the water, otherwise they’d have to up and down in the water column. 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 fishes’ 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 to inflate their bladder. The physoclistic bladder is closed off and can only add or vent gas through the blood via the gills. This doesn’t happen very 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 Tessellated Darters, Long nose Dace and Mottled Sculpin.Reef fish have a closed swim bladder and it expands rapidly (about 25% for each 30 feet of depth) and so fish brought up quickly from deep water will not be able to equalize their bladder. If these fish are released they 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’s possible to puncture the air bladder, which allows 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 most often an excessively inflated air bladder. This may result in a swollen abdomen or the air bladder forcing the gut lining to protrude out of the mouth.Piercing the gut lining sticking out of a fish’s mouth will not deflate the bladder. It will cause a tear in the gut wall and allow water to get into the body cavity of the fish. This would most likely result in the death of the fish.Bladder deflation by the angler can be done with a sharpened basketball inflator probe or a large gauge hypodermic needle. These are much better than a wire or knife as they are easy to obtain and allow the angler to hear the hiss of escaping air when venting is done correctly.In red snapper the needle should enter 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. Do not enter too high up on the body or you’ll 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.Fish swim bladders in the past 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 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 then cut into thin translucent strips.These strips, which are nearly 80% 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% and is degraded by UV light. Other uses for isinglass are as a clarifying agent in the beer and wine production, handmade paper, inks and special paints and anywhere gelatin is used (jelly).
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