I would suggest visiting this museum located in Al Khan, Sharjah. There are a bunch of tourist hotels located nearby to this museum. A Maritime Museum located adjacent to it, will be launched in 3 months.
The museum has two floors charmed by exuberant ambience, a small cafeteria and a goodies shop. Once you are done with the museum, you can walk across the new Sharjah corniche. The authorities are also planning to have a boat ride across the Sharjah lagoon in the near future. The place is worth a visit and much better than the Dubai Mall aquarium which is slightly more.
A quick comparison of prices with the Dubai Mall Aquarium: -
Sharjah Aquarium
Adult20 AED/Child (6-15) 10 AED/Child (5 years old &under)Free
Family (2 Adults & 3 Children)50 AED/Adults Groups (6 or more persons) 15 AED
Child Groups (6 or more persons) 5 AED
Dubai Mall Aquarium
Entrance to the Dubai Aquarium Tunnel
Child AED 20 /Adult AED 25
Entrance to the Underwater Zoo & Tunnel per person - AED 50
Sharjah Aquarium
Adult20 AED/Child (6-15) 10 AED/Child (5 years old &under)Free
Family (2 Adults & 3 Children)50 AED/Adults Groups (6 or more persons) 15 AED
Child Groups (6 or more persons) 5 AED
Dubai Mall Aquarium
Entrance to the Dubai Aquarium Tunnel
Child AED 20 /Adult AED 25
Entrance to the Underwater Zoo & Tunnel per person - AED 50