Leon Valley Police Chief Joseph Salvaggio said the pair put the shark into the bag and then a bucket hidden inside a baby stroller.
In a Facebook post, the San Antonio Aquarium said an employee saw the man take the shark out of the water and alerted management. When the men tried to leave, a manager asked if he could search their vehicle, but the men refused and left.
Aquarium employees noted the men's license plate number, and authorities quickly located the suspected shark snatchers. The shark was recovered in good health, as police said the suspects had experience with marine animals and placed the shark in a proper environment.
"Luckily the thief was someone who knew what he was doing," Salvaggio told KABB-TV.
A local ad for a shark for sale may be related to the case.
The shark was returned to the aquarium. The suspects face felony charges for theft.
