If you go to www.mywildalberta.com and pull up "Fish Handling Techniques" the following are some of the comments on protecting fish from injury.

Safe fish handling is especially important in a catch-and-release fishery. Catch and release regulations are in place to help fish populations grow when they have been overharvested, or when the water body needs time to establish health and productivity.
Releasing a fish doesn’t guarantee its survival, but careful handling can reduce the stress on fish and gives it a better chance to live and reproduce.
Walleye and perch have a reduced chance of survival if they are caught in water deeper than seven metres, brought to the surface, and then released. When walleye or perch are caught in deep water, their swim bladders can’t adapt quickly enough to the change in atmospheric pressure. This causes the fish equivalent of ‘the bends’. The internal damage that results will likely kill the fish.
If you are fishing deep water, and catch a prohibited fish, it must be put back, even if it dies. The sportfishing regulations state that you must release every fish that cannot be legally kept because of species, catch limit, size limit, or other regulations, without exception, even if the fish is injured or dead.
Walleye and perch should be fished in relatively shallow water, where there are great angling opportunities.
Walleye and perch have a reduced chance of survival if they are caught in water deeper than seven metres, brought to the surface, and then released. When walleye or perch are caught in deep water, their swim bladders can’t adapt quickly enough to the change in atmospheric pressure. This causes the fish equivalent of ‘the bends’. The internal damage that results will likely kill the fish.
If you are fishing deep water, and catch a prohibited fish, it must be put back, even if it dies. The sportfishing regulations state that you must release every fish that cannot be legally kept because of species, catch limit, size limit, or other regulations, without exception, even if the fish is injured or dead.
Walleye and perch should be fished in relatively shallow water, where there are great angling opportunities.
A fish with a swollen swim bladder will have sides that are hard where they should be fleshy, or will have the swim bladder protruding from its mouth. If you wish to release a fish with a swollen swim bladder, do not fizz it (poke a hole in the swim bladder so the fish sinks). Fizzing does not increase survival, but causes injury, stress, and almost certain mortality.
Fish with swollen swim bladders should be released gently into the water. With enough time, a swollen swim bladder can correct itself. The fish may float belly up on the water, but it has a better chance of survival if left on its own.
When fishing where there is a size limit, carry a measuring stick. Leave the fish in the water and hold the stick beside it to determine if it’s legal length. If it is legal length and you are keeping it, hold the fish in a rubber mesh net or a holding cradle to measure it again to ensure it is legal. If it’s not legal length, gently remove the hook with needle-nose pliers and release the fish.
Remember the 'fair chase' principle: minimize the time that you handle the fish once it is on the hook. Handling a fish to exhaustion may cause it to die later.
Keep fish in the water while handling and releasing them. If you must handle fish, completely wet your hands or wear soft cotton or wool gloves that have been soaked in water. This prevents damage to the fish's protective mucous surface.
Act quickly by having your measuring board or camera ready if you must measure or photograph your catch. Minimize the time the fish is out of the water.
Prepare in advance to release your fish by choosing a hook that can be removed from the fish's mouth easily or use landing nets when they help quick release. Use needle-nose pliers to remove hooks and never tear a hook from a fish. If the hook is deeply embedded in the fish's throat, snip the line and release the fish, leaving the hook in place. The hook will eventually dissolve.
When handling a fish that is to be released, be gentle. Don’t squeeze the fish or put your fingers in its eyes or gills since this increases mortality. Limit the time the fish is out of the water, and whenever possible, unhook the fish without removing it from the water.
When releasing a fish, never just throw it into the water. If you have to handle a fish, release it gently and headfirst. A fish will often swim away on its own. If it doesn’t, hold the fish gently in front of its tail and slowly move it back and forth to push fresh water over its gills. Release it when it begins to swim away.
If the fish will be used for food, dispatch it quickly and keep it on ice.
Holding fish in a livewell or on a stringer with the intention of releasing them once a larger fish is caught reduces survival rates after release. Studies show that mortality of released fish significantly increases if they are held in rough and/or warm waters. If you plan on keeping a fish, you should dispatch it quickly and keep it cool, preferably on ice.