Well its hard to answer since all phobias are very specific, but i think i might know what youre afraid of.
Ichthyophobia- is the fear of fishes
Fear of water is very natural; you arent the only one. Make sure while being near aquariums, to relax and not be tense about it.
The real problem is when you let fear overtake you to loath of doing anything worthwhile.
You must and i repeat, you should constanly visit aquariums, even if it's the most irrational thing that sounds like you should do; but visit as many places that have aquariums.
You should also, try to record yourself saying you arent afraid of aquariums, and listen to your voice. Think about you walking into a aquarium and the glass completely breaking and all the water falling out; so when you are near one, you know that would be very unlikely to happen.
Other than that; the only way to overcome your fear is by facing it.
"there is really no FEAR without belief".