My mother owns two
goldfish, both "feeder" comets, the oldest of which is 5 years old. Both have lived in seperate bowls their entire lives, and while both have done well somehow despite not having adequate filtration and space, kinda feel bad for them, especially since my babies are so spoiled.
Make no mistake--my mom treats these fish well and they've been healthy save for the odd swim-bladder issue here and there. How this happened I don't know, since all that I've ever read says the setup they're in means death
However, mum has recently decided that Gromit (the younger, smaller one) needs a bigger home, and I've been using this to try and get her to purchase a nice, 10 gal+ tank with filtration for them. She's reluctant despite my saying I'd buy it for them, mostly because she's worried that Gus (the older one) will harm Gromit. Now, goldies are social fish, and they are very similarly sized fish, but they HAVE lived alone for their entire lives.
Would fish-harming-fish be a concern? Obviously they'd try to establish a pecking order, but would it continue beyond this?