Since you are 16, I'll give you a little unsolicited advice from a guy who's 30 and still dealing with a Dad who is "always right."
1) Your Dad is human. He makes mistakes, don't take him to task, talk to him like an adult with facts and reasonable opinions to sway him to your thinking. Like my Grandmother always said: "You catch more bees with honey than vinegar." I'm sure you get the point.
2) Admit that he might be right sometimes. You'll get along better.
3) Someone already mentioned this, but point out that you are a good kid who does his schoolwork and doesn't do drugs ad other bad crap. Fishtanks are a healthy hobby.
4) Enjoy the time now, you grow up and go to college, then you have to work in the real world, it sucks, and makes people irritable. Fishtanks become less of a priority.
Now go start planning your 180!