SKJERJEHAMN, Norway — As a teenager, Ola Braanaas kept a few fish in an aquarium in his bedroom. Now, at 55, he keeps a lot more of them: around 1.2 million just in one windswept spot off the stunning coast of Norway, a giant farm with six large, circular structures each containing around 200,000 fish.

Once a rarity on global dinner tables, salmon is a staple today, thanks to a fish farming industry that has expanded at breakneck speed in recent decades, including in Norway, where in 2016 around 1.18 million metric tons were produced.

But now, Norwegian fish farmers face new curbs designed to protect the country’s stocks of wild salmon, rules that have ignited anger from the industry and its opponents, prompting threats of court challenges from both sides.

The wild Norwegian salmon are members of an ancient species that, early in its life cycle, heads down river, swimming through Norway’s famous fjords, and out to saltwater feeding grounds, before returning to their native rivers to spawn.