Rapid removal of fish from deep water to the surface by traditional angling techniques does not allow an ample time for depressurization. Effects of depressurization can include, over inflation of the swim bladder, inability to submerge when released,abnormal swimming behavior, eye bulging, gas bubbles in the blood, organs protruding through the mouth, and death. Other factors include stress of the fish due to a number of issues. These issues include the following; Time it takes to land a fish, the longer it takes to land the fish, the more stress it experiences, just like us, fish build up lactic acid in their muscles when they use them. This acid is what makes our muscles sore the day after we work them hard. Hooks and lures play a role in stress as the fish thats hooked in the front of the mouth does not have the stress put on them that a fish that swallows the hook, or gets a hook into it's gills. Temperature will also effect the stress level, the warmer the temp the more stress to the fish. If you hook a fish that is in deeper water that is cooler, and you bring it to the surface where the water is much warmer, you will increase the stress level.
Changes in depth rapidly will cause a high level of stress in fish. Fish have a gas bladder that enables them to adjust their buoyancy and depth much like a submarine. Pressure increases as water depth increases. A fish caught in 30 feet of water and is brought to the surface will have it's bladder expand quickly and double in volume putting severe pressure on the internal organs. A fish caught in 60 feet will have a great chance of the bladder protruding out of the mouth and the eyes buldging from the head.
A fish that is unable to swim upright in the water because of high stress and or overinflated bladder, stands a poor chance of survival if released. "Fizzing" is a technique where the gas is released from the bladder by insertion of a needle.
Following are the techniques used to "fizz" a fish.
I perfer the through the mouth technique, but you must becarefull as you may puncture the heart. If you have addressed the fish and feel that "fizzing" is needed
hold the fish by the lower lip and look straight down it's mouth, you will see the "crushers" in the back of the throat. Locate the horizontal line formed by the "crushers" and insert the needle just above the line ( see photo) . You will feel a slight pop when you have entered the bladder, submerge the fish under water and watch the gas bubble out. You DO NOT NEED and SHOULD NOT let all the gas escape. You only need to let enough gas out to allow the fish to stay upright on it's own. If you allow all the gas to escape, the fish will not have any buoyancy and will lay at the bottom not being able to swim very well.
The second technique is to "fizz" through the side of the fish. In this technique you must take care not to puncture the kidney or intestine. To complete this technique you will draw a verticle line from the notch formed by the dorsal fins to the anal vent. At the intersection of the lateral line and the line you have drawn you will move down to a point approx. 1/2 inch below the lateral line, at that point, you will lift a scale and insert a needle under the scale at a 45 degree angle towards the fish's head. As you insert the needle you will feel a pop when you enter the bladder, and hear the gas escaping. Hold the fish upside down under the water and watch the gas bubble out. You may be required to gently squeeze or stroke the bladder to use this technique. Again you DO NOT and SHOULD NOT let all the gas escape from the bladder.
Here are a few suggestions to help with your catch
1. Continuously run the boats freshwater aeration system to introduce new, fresh water into the live well

2. Lower the temp in the livewell by adding ice, frozen water bottles work well for this

3. Use an oxygen injection system ie. Keep Alive, Oxygen Edge or Pure Oxygen are a few to look at.

4. Add noniodized salt to your live well to achieve a .05 percent solution.
(approx 1/3 cup per 5 gallons)

5. The use of water conditioners made for live wells such as Rejuvenade, Please Release Me. Most of these conditioners add compunds to allow the water to hold more oxygen, as well as relax the fish and protect the slime coat.

Hope this will help you with some understanding and ways to keep your fish alive and healthy.