I don't normally feel sorry for my own fish, except for that big hybrid african I have in a 75, (he was in a 55, and at 8 inches long it was a bit small) and I don't really feel that bad for him either. He has a tank with only catfish as tankmates, he gets good amounts of food, and he is in a tank he can freely move in, for a hybrid some would have culled at hatching or before, that isn't so bad a life.
I try to keep to fish 6 inches or smaller, or even better the ones that normally defend small territiories. If you buy a saltwater fish that naturally lives in a burrow, and defends a stretch of sand a foot wide, life in a tank is not that different from home, except with fewer critters trying to eat you.
I do however feel very sorry for certain varieties of salt fish, and fresh. Pretty much anything that maxes out to over 12 inches and swims a lot. Sharks, Rays, Groupers, ID Sharks, Morays, Balas, Tinfoil Barbs, Arowanas, Peacock Bass, Oscars, Red-Tailed Catfish. The things people pick up as cute juvies then return at a foot complaining that they keep trying to jump out of the 100 gallon tank....or maybe their 10 gallon depending on the people...
I don't even really feel sorry for my cockatiel. Someone dumped her at a local pet store and I adopted her. She was a hand raised bird, and wouldn't have ever really done well in any "free" situation or any only caged situation either. She wants to be with people. Yes, she spends a lot of time in her cage, but she also gets at least an hour a day of free time, which means climbing all over me, the room, the outside of her cage, my desk, and whatever else she can get to. If I was to feel sorry for any of my pets, it would be her. If I had the space i.e. an extra room, I'd set her up in a room of her own, with no space limits besides the walls. If i had the space I'd also liek to do that with an iguana.
--Mia