To help you with your dream - when you're ready to move out, read the apartment contract carefully. Many places won't allow fish tanks, so you want to be sure to go to a place that does. 
I feel the same way, but my husband and roommate are WAY more tolerant than your sister. They're happy I want a hobby, but (rightfully) nervous that I'll take over the house with fish.
I feel the same way, but my husband and roommate are WAY more tolerant than your sister. They're happy I want a hobby, but (rightfully) nervous that I'll take over the house with fish.