here's a little bit about weighing your trophy with your boga and then releasing it (this was for muskies, but i think a lot of it applies here):
The Risks of Vertical Holds:
1. Muskies lifted by a gaff or suspended for weighing from the tip of the lower jaw risk internal separation of the connection between the two halves of the lower jaw (it is a two piece bone) and this will prevent effective feeding after its release.
2. It has been reported that big largemouth bass when held unsupported by an exaggerated lip lock have suffered jaw damage. Now consider a 15 to 40 pound muskellunge - its jaw and associated muscles and ligaments were not constructed to support that weight under the influence of gravity.
3. The V-shaped connective tissue on the underside of the head comes under significant stress (stretched and distended) when absorbing the unrelenting weight of the fish's torso. This are is attached to the gill arches and delicate vascular tissue which, if damaged could result in the death of the fish minutes after release.
4. The cervical vertebrae (the sections of the spine connected to the skull) are subjected to enormous strain making likely nerve damage. Under the influence of the weight of the body, it will bend backward and twist in unnatural ways. A thrashing muskie will strain the delicate nerves in a range of directions,
5. Another fairly evident problem with vertical holds is organ slippage. Within the abdominal cavity, the liver, kidneys, heart, gonads, and GI tract are held in place by membranous connective tissues. Within a vertically held muskie, the force exerted by some of these heavier organs will result in these tissues stretching and tearing as the organs slide back toward the pelvic fins.
6. Any time a fish is lifted vertically, there is a greater chance that the it will be accidentally dropped. The result is a fish banging around the bottom of the boat. The consequences of this include internal injuries as well as loss of the protective mucous and damage to the cells that produce it.
the other side to this is, what somebody else said: that the released fish still has a better chance than if it was in your fishbox. also, all of this is basically anecdotal. havent seen a good well designed study yet. meaning there is no real statistical evidence that these things are true. the study maybe out there, but i didnt find it.
despite all that, i can probably believe holding big fish vertically isnt good.