A diver maintains an open-water cage where tuna are being farmed in Izmir, Turkey. In the U.S., federally controlled ocean waters have been off limits to aquaculture, curbing the industry’s growth. But the tide may be turning.

A diver maintains an open-water cage where tuna are being farmed in Izmir, Turkey. In the U.S., federally controlled ocean waters have been off limits to aquaculture, curbing the industry’s growth. But the tide may be turning.