I had this discussion before when I used to keep rats. For a different reason.
The thought that keeping rats could be a hobby insulted some of them.
I didn't know what else to put the expenses under.
Career, health, educational expenses ( yeah I was in college at the time) or basic necessities...So since I kept rats for pleasure and not to make money or to fill basic needs, then it's a hobby?. I guess for some of them keeping rats meant the rats were family members now and I was objectifying them.
Feel the same way about the fish unless they are a source of income or I'm going to do something functional with them like raise them for food.
And to answer the basic question here, I see them as both.