I don't ascribe feeling to fish like they are dogs or people, but I do think it is our responsibility, if we remove them from their native homes, to provide the best possible environment and food. Otherwise, leave them be. That's where the Tang Police in me comes out.
I can only say, for me, that my tangs will live out their full lifespans of almost 20 years, are fat and glossy and swim calmly. This is a direct result of observing them for 30 years and figuring out what they require both nutritionally but psychologically as well.
As your photo shows, they tend to school in order to feel safe. Some tangs go it alone, but all living creatures want to feel safe. In the case of inter species predation, getting out of the line of sight of the predator fish is step one, they have to have a safe area they can hunt in and feel they can easily escape a sneak attack. That's just a small part of what tang psychology entails. JMO