Zen, maybe we can equate this fish to a blackmouth (resident king salmon). Blackmouth do not migrate to rivers in the fall. They grow up in salt water and stay in salt water. There energy is spent on feeding. When you catch a blackmouth they are usually shaped like a football, narrow at the head and tail and full of girth in the middle. They are also shorter in length than migratory fish. A migratory king will be longer from head to tail with out a gut. More symetrical I guess.

This is just a theory.