I normally only fish blues in winter on the James river. It seems their skin is very tender and the net often scratches them. If we get then from deep water we will burp them with a piece of PVC so they can get back to nuetral bouyancy. If catmen don't vent fish from deep water they often flounder on top trying to get back to the depths. Expanded air bladders can keep them from working their gills and they die if not vented.
Then a couple of quick photos and put them back in the water and hold their tails till they kick free.
For flathead I wet my sling then quickly put the fish in weigh slings and weigh them.
This supports the fishes weight and they are calmer when being weighed. You can use your landing net if you don't have a sling.
In warmer weather watch your flathead. When they start turning yellow it is a sign they are getting hot and need oxygen. Always keep fish wet.
Put them back into the water and hold their tail till they kick free. About half the flathead swim away slowly but they are OK. The large flathead are used to moving slowly and don't get in a hurry even when leaving.
Don't lift by the gills. I've caught a few large flathead with broken jawbones. Not sure if they escaped limblines with the injury or were held by the jawbone for pix and thrashed and broke the jaw.
Make all attempts to remove hooks. On big fish you can reach into the mouth and reach anywhere the hooks go. Remove any other hooks that a fish may have in them. We all know the hooks will rust out but it is much easier on the fish to have them removed.
When you hold large fish for pictures support their weight as much as possible. Return your fish as soon as possible to the water.
Well where to begin? Landing a large fish requires a large net. I admit I have squeezed some cats into bass nets before, but it really rips the slime off of them. Also keeping your net wet helps in minimizing the removal of the fish's slime that protects it from harmful bacterial disease. I usually leave the net sitting in the water. When weighing a large fish its better for the fish if you weigh the fish in the net or in a sling. This keeps the pressure of the fishes weight evenly distributed over the entirety of its body rather than its gills. When taking pictures its best to cradle the fish with both hands, one in the mouth and the other near its anal fin or belly. I have read that holding a large fish by its mouth can tear its gill arch. Holding a trophy flathead by its mouth tend to produce better pictures though, so I usually try to minimize the amount of time the fish is suspended by its mouth. One of the worst ways to hold a fish is by holding them underneath their gills.