I treat all of my fish with the same care, no matter the cost of the fish or the care. Who said livestock! Yes they are livestock, some individual specimens get a name though naming a shoal is silly!
(Saying that, my C. agassizii shoal is the spaghetti mob!)
They have Latin names. That's all you really need.
I have bred feeder fish for a bichir, those platy were treated exactly the same, a tank with plants etc. just one day they go for a little walk. If you keep piscivores it is only fair to feed them properly. (Actually it's quite exciting if a little barbaric)
Equally, I will do what I think is necessary when the time comes.
How I do it is personal and not a subject for conversation. It is quick.
I find a fish that I've kept longer is harder to dispatch. Once it is netted and a decision has been made that is it, done. I hate killing fish but sometimes it is required. I always exhaust all other possibilities before I choose this route. Sometimes there really is nothing you can do except what is right.
If a fish dies in my care I always take the time to consider myself and whether or not I could have done things different, sometimes a fish is just old, sometimes it is my fault and sometimes it is neither.
Cost is irrelevant! If I was worried about the cost, I'd pack up and shut down tomorrow. The entire hobby is really a waste of my resources, but you get a lot of return on your investment! It's a shame joy and pleasure have no official measure.