we went today to the Sharjah Aquarium and Maritime Museum. The entrance fee is 20AED per adult and children 6-15 pay 10AED with kids below free.
The Aquarium is quite nice even if not really big. With the entrance fee paid for the Aquarium get also free entrance to the Maritime Museum which is directly next to the Aquarium and well worth a visit..
More infos: (LINK)
The Aquarium is located direct on the seaside: