It's good that you're thinking ahead, but it's definitely not an easy thing to do. I did it with 6 of my ball pythons. One was in a 15-gal tank, the others were in tubs. You really can't do it without the full consent of your roommate(s). I asked my roommates before I even bought my first snake 6 months before we moved in if they would be okay with it. And even then, after a year of living with my snakes, there were several times in which they threatened to have them removed while I was away. At that point, I moved out of my room and lived 20 minutes away at my friend's mom's house to protect my snakes. Not trying to scare you, but want you to really think about the fact that it's not an easy thing to do. On that note, they also got me through the toughest year of my life (I only had them during my senior year). There's nothing like taking a break from the hell of studying and just having a moment holding your snake. Best stress relief ever.

However, if your future school is like most schools in the country, you will not have a car for your first year (some places, like where I went, you wont be able to have a car until your junior year). How will you get to the nearest pet store easily when you run out of mice/rats? What if the snake ever got out? My school had cleaning ladies come into the rooms weekly along with monthly health and safety inspections - all times when I had to make sure everyone was hidden. There were times when things in the room broke and repair guys had to come in to fix them when I wasn't there - queue the frantic calls to the roommates to make sure my kiddos where out of sight or sprinting to the room between classes to do it myself.

In addition, it was absolutely critical to me that no one outside my roommates and one or two trusted friends knew my snakes existed. These animals' lives are in your hands, so it's up to you to make sure they wouldn't be caught and confiscated or whatever might happen (I don't have a clue - hopefully they'd just tell you to get them out and you'd take them right back home and pay your parents lol)

Anyway, I didn't mean for this to be a huge intimidating chunk of text, just want to get the gears going in your head. Very good thing you're starting to think about it now, but the fact that you are trying to "hide" something forbidden is an indicator that you know it's wrong And fish shouldn't be a problem. Most schools allow freshwater tanks 10 gal and under.