How do aquarists train wild caught fish to accept foods after being collected from the ocean?
You got to be specific, as to which fish? Some species are easy, other species are not.
Basically, you keep them comfortable and feed them replica of what they eat in the wild. Once they eat, you can mix the food they eat with suitable type of food that you want to provide for them in aquarium. The ratio of these change slowly until you can convert to aquarium food.
Having dither fish works for me in getting hard to keep fish eating, along with having a natural setting. I keep a 40 gal reef with lots of LR, LS and fauna and flora. In this tank most fish are very comfortable, and will start eating quickly. Seeing other fish eat will really help as they learn from other fish much easier than finding out themselves.
Right now I got a pair of tiny Leopard Wrasse, only about 1.25 nad 1.5 inches long. I only had them in there less than 1 week and they already eating pellets (Otohine pellets on automated feeder) These guys are too small. They likely will become Harlequin Tusk (My tusk is 6.5 inches) food if I add them into my DT right now. I will keep them in my QT system for several months to grow them out first.
A strong warning on QT prior to add animals to your system.
My method works for me. It is not conventional. I don't QT or prophylactic treat my fish for disease. I don't care that I add Ich to my tank. I don't use garlic, and Ich never get a foot hold in my tank. Other than Ich, I don't add obviously sick fish into my tank. My QT is only strictly get the fish comfortable, eat well and gain weight prior to add him to my DT so he can fend for himself.
My method rely on the health of the fish and it's immune system. It rely on the very diverse Fauna in my tank eliminate diseases as it is in the wild. This does not work for everyone. My DT is a large 320 DT with 100+ gal light sump absolutely full of diversity. Trocus and Turbo snails breeds in my tank. A large numbers of smaller snails also reproduce in my tank along with Chitons. I took lots of steps to ensure the diversity of fauna in the sand bed and the rocks.
If you have a relatively sterile system with minimal fauna, this method (no QT) will not work, and you will be in for a lot of heart aches and tank wipe out if you trying to do as I do. With this method, I am able to keep sensitive, hard to keep fish with ease. If you rely on medications and QT/Hospital tank to eliminate diseases first then add the fish into your DT, then you will need to accept that there are hard to keep fish that you cannot keep.