Watching flamboyantly colored fish flit about a saltwater aquarium can be relaxing. Figuring out where they came from, and whether they were caught in a sustainable manner, can be an exercise in frustration.

The aquarium trade is a global industry with no centralized database to track what gets bought and sold, and with no central governing body to enforce regulations. Collectors and exporters in places as far-flung as the Philippines, Sri Lanka, and Florida pump tens of millions of marine animals—more than half of which end up in the U.S.—into the multimillion-dollar business each year, often with little or no oversight.

About 1,800 tropical fish species are involved in the international trade, says Andrew Rhyne of the New England Aquarium in