The image is optional
For a fish that will be released, have the camera ready before handling. Keep the animal wet and supported, minimize air exposure and skip the photograph when the fish is distressed.
A water-level or partly submerged frame can preserve useful markings without lifting the fish far from the surface. Local rules and species-specific guidance take priority.
Record evidence quickly
One whole-body side view, one close frame of the head and one image of the relevant fin or tail are usually more useful than repeated portraits.
Wet hands and appropriate nets help protect the surface of the fish. Avoid the eyes and gills, and support the body rather than suspending it.