Looks like a bacterial infection that started with an injury. I stopped using treble hooks years ago if that is what started it. A gang of treble hooks on a plug is even worse. They really cause a lot of damage to a fish.

There are some bacteria in the water that will literally eat the skin right off of a fish. Even though these bacteria are usually present in the water at all times, they only cause problems if the fish is injured or its immune system is compromised.

As far as relative weight I'm with Sunil. The fish looked otherwise healthy.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.