1. Wet your hands
Before handling a fish the first thing you should always do is wet your hands. Fish are covered in a layer of mucoproteins - what most people know as "fish slime." This slippery product is actually a protective barrier, essential for shielding fish from bacteria and infections. Contact with dry surfaces can remove this barrier and make fish more susceptible to illness. Wetting your hands before handling a fish will greatly reduce the amount of slime that is removed.
Another culprit for removing fish slime is nets. Nylon and mesh nets are highly abrasive and can tangle easily around a fish and its gills. A rubber net is a must-have for sustainable anglers, as they are much softer on the fish and won't remove the protective slime.
2. Minimize Air-time
Fish get tired too, and like humans, they need oxygen to recover. Holding them out of the water after a hard fought battle only adds to their fatigue and can have fatal consequences if held out for too long. Try to keep the fish in the water during the entirety of the handling and hook-removing process. A partially-submerged rubber net is a great place to remove the hook while keeping the fish corralled and wet.
If you must remove them from the water, do so as quickly as possible. Less than 10 seconds at a time is generally a good rule, as periods longer than that can have long-term recovery impacts.
3. Keep them horizontal
Fish spend their entire lives suspended horizontally in water and it's important to maintain this during the handling and release. Holding a fish vertically can disrupt their equilibrium, break their jaw or disturb their internal organs. It's particularly important not to hold them vertically when lifting a fish out of the water, as the sudden change in gravity from water to air can have serious impacts on the internal structure of the fish. Contrary to popular belief, even freshwater bass should be held horizontally, especially when over several pounds.
Keeping them horizontal is important when reviving fish as well. In moving water, point the head of the fish against the current so the water runs over its gills. You'll feel it give a "kick" when its ready to swim away on its own. In still-water situations, give the fish a gentle push to get it swimming again.
Hurry up and the take the photo!
Catch-and-photo-release is a great way to remember your day on the water and promote the sport of fishing. But the health and revival of the fish should never be comprised for the sake of a photo. Make sure your hands are wet and hold the fish horizontally a few inches above the water, a still dripping fish makes for a much better photo anyway.