Since, Im a marsh member I will chime in.

Not much on the North Side.

West Side
City Pets is at Beltway 8 and Beechnut.
Global in on Bellaire, go east from the Tollway
T&T is on Highway 6 and Bellaire (same shopping area as CiCi's Pizza)

Central
Fish Gallery(59&Kirby, next to Academy Sports & Outdoors)

SouthSide
Bay Area Aquarium(near Nasa)
All About Fish
Megans Tropical

check out the marsh Website www.marshreef.com