"Fizzing” or releasing the pressure from the gas bladder is sometimes used to facilitate release of undersized fish. "Fizzing," when done correctly, is a process where gas is released from the gas bladder of a fish by inserting a needle in the side of the fish and puncturing the gas bladder. Many anglers who practice fizzing are actually puncturing the stomach. In actuality, it is the pressure in the gas bladder that must be released.

A fish that is unable to remain upright in the water because it is severely stressed and/or has an over-inflated gas bladder, stands a poor chance of surviving if released. While helping a fish regain its ability to return to the bottom of the lake, many fish that are "fizzed" end up dying within a few days of release, from the stress of being caught and handled. There is also the likelihood that when you insert the needle into the side of a fish you will damage internal organs such as the kidney or intestines.

When a perch is quickly brought up from depth, the stomach is forced out through the mouth as the gas bladder expands from a decrease in pressure as the fish is brought to the surface.

There are two major different types of gas bladders in fishes: physostomous, in "primitive" fishes and physoclistous, in "derived" fishes. Your understanding of lake trout physiology as related to the air bladder is correct. Lake trout are among the generalized fishes known as Physostomi, which have a direct connection (pneumatic duct) between the air bladder and digestive tract. This duct facilitates the direct passage of air in either direction. Typically, this group of fishes fill the air bladder by gulping air form the surface and release air from the bladder by “burping.”

Physoclistous gas bladders, however, do not open to the mouth, so the fish has to let gas in and out of the bladder using a very complex little patch of blood vessels that absorb or let go of gases from the blood. Fishes with these bladders include bass, perch, and sunfish.