Considerable time and care should be exercised when releasing fish. First, when possible, release fish in areas away from predators. During the fight and landing, there is a short term accumulation of lactic acid and stress hormones in fish muscle that makes it more difficult for them to evade predators after release.
Fish should be placed in the water and held by the base of the tail. If the fish does not swim away from your grasp on its own, gently move it forward in the water to get water flowing over the gills.
For best results, move the fish in the forward direction only instead of back in forth. A fish’s gills somewhat resemble the pages of a book and are designed for water flow in only one direction. Moving the fish in a slow circle or gently towing it behind the boat will accomplish this.
Info from IGFA’s website