While a growing number of Americans are paying close attention to traditional livestock — demanding more organic meat, cage-free eggs, and grass-fed beef — not as much attention has been paid to the massive global market for seafood, and the ethical, financial, and environmental impact it has.

For The Fish on My Plate, the latest documentary from PBS’s Frontline, author Paul Greenberg set out to answer some questions he had about consumers’ relationship with seafood, namely, “What fish should I eat that’s good for me and good for the planet?”

The result of Greenberg’s investigation airs tonight, and we highly recommend checking out the entire documentary. here are some of the bits we found the most fascinating.

1. Americans are the second-largest consumers of seafood in the world: And the average piece of seafood served in American restaurant travels 5,000 miles before you take a bite. Up to 90% of the fish we eat in the U.S. comes from abroad, while we send about a third of what we catch to other countries.

2. Beware of smelly fish-oil capsules: Up to 20 million Americans take fish oil as a supplement, but because the omega 3s in this oil are active compounds that spoil fast, seafood processors have to work quickly. A poorly processed fish oil capsule can rot, just like a fish. Even if you doubt that Omega 3s have real health benefits, Greenberg points out that “a rotten oxidized capsule does nothing” for you.

3. Where’s my fish from? The world’s four million industrial fishing vessels can net half a million pounds of fish in a day, not all legitimately. With such a huge amount of seafood, it can be hard to figure out what it is and where it comes from.

For example, a “wild” salmon product Greenberg encounters at the Boston Seafood Show, that’s labeled as a product of China: The “raw material” — in other words, the fish — is from the U.S., a company rep explains to him. It’s frozen and sent to China, where it’s processed and cut into filet portions “with some other species,” and then it’s exported back to the U.S. again. Yes, that means it’s frozen and defrosted twice before reaching your plate.

4. Almost half the fish we eat is farmed: Norway is known as the birthplace of modern “aquaculture,” where five families control most of the industry in the country. On a visit to one salmon farm, the owner notes that there are around 20 million fish in feed cages.

5. The largest fishery in the world raises fish for feeding other fish: The anchoveta, one of the smallest fish in the sea, is raised at the world’s largest fishery, a facility in Peru. But instead of feeding people, 99% of the anchoveta catch is turned into fish oil and fish meal used to feed other fish.

6. “Feces Theater”: Conservationists cite problems that plague fish farms. Sea lice — which can be lethal to juvenile fish if enough of them latch on — can breed and spread not only in pens filled with fish, but can then spread to wild species and and continue to wreak havoc.

Then there are all those droppings from all these millions of caged fish: One Norwegian critic who calls himself an “eco-warrior” is on a mission with his group, Green Warriors of Norway, to show the public what he calls the dirty side of the business.

He films fish droppings with a remotely operated submersible, and pipes a live feed from under working farms to show audiences in a specially-built theater on his ship. He calls it “feces theater.”

7. Fish are resilient, if we can just leave ’em alone: As conservationist Carl Safina notes in the documentary, compared to most problems, overfishing is “quaintly simple.”

“You just don’t kill them faster than they can breed, and they will start to get more of them. It’s not complicated,” he explains.

But it’s not always easy to convince people to ease up, especially in parts of the world where there is no rule of law. If there aren’t rules, or they aren’t enforced, there’s also usually corruption and little to no political will to change things.

When it comes down to it, there seems to be a lot of talk about sustainability and responsible farming — but there doesn’t seem to be a clearcut consensus on how to do that while also meeting the world’s demand for fish.

Check out the entire Frontline tonight on PBS, airing at 10 p.m. ET and online.

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