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Facts about the virtues of eating fish can be slippery. On the one hand, fish provide protein and omega-3 fatty acids, the substance in fish oil supplements, which is thought to boost cognitive health. Plus, 

, fish don't belch vast amounts of the greenhouse gas methane into the air. So, fish should be good for your health and the environment. But the science of omega-3 benefits is 

, and as fish farming grows to keep up with global demand, the industry is raising new questions about environmental sustainability.

New York Times bestselling author and avid fisherman 

 wanted to learn more about how eating fish can change human health and the world's marine environments. He ate fish every day for a year to see how it would affect his health and traveled around the world to learn more about the challenges of fish farming. His experience is captured in a FRONTLINE 

 called The Fish on My Plate airing Tuesday. (You can also watch it online.)

We watched the film and talked with Greenberg about what he learned while making this documentary. The conversation is edited for clarity and concision.

As a fisherman who enjoys catching food from the wild, do you think we need fish farming?

If everyone's going to be a vegan, no, we don't need fish farming. If we want to have animal protein in our lives, then yes, I think we do need it. People often compare wild fish to farmed fish, but what we should really be doing is comparing fish to other forms of protein. Because things like beef really are a tremendous burden on the planet in terms of resources, we're never going to get to the place where everybody on the planet can eat beef. But I do think we'll get to a place where everybody can eat mussels.

Only eating wild fish doesn't work with the equation right now. We're catching 80-90 million metric tons of wild fish per year, and that's not going to meet the protein needs of the world, plus it's putting a lot of pressure on fish populations. I'd rather see that need met through aquaculture [fish farming] than through more beef, pigs or chickens.

What makes a fish a good candidate for aquaculture?

Some criteria are a general adaptability to confinement, a resistance to disease, the ability to produce a lot of offspring, and fast growth. And you see fish with these traits rising to the top of fish farming. Take tilapia. It grows very fast, from an egg to an adult in nine months, whereas a salmon can take 2-3 years.

That said, people like some fish more than others. So there are efforts in aquaculture to tame certain fish [like salmon] because there's a market for it, not because they're the best suited for farming.

The film shows that fish farming is far from perfect. What are the biggest challenges facing fish farming?

It's what the farmed fish eat and where they live.

We tend to prefer carnivorous fish like salmon, and they like to eat other fish. So roughly 20 million metric tons per year — a quarter to a fifth of the global catch — goes into catching fish like anchovies that are ground up and fed to other fish. Salmon farming has become more efficient over the years through selective breeding and improved farming techniques. It used to take six pounds of wild fish to produce one pound of farmed salmon; now it takes less than two pounds of wild fish. But at the same time, the amount of farmed salmon that we're growing is increasing, so the pressure on these small wild fish continues.

This problem is being worked out in techniques using other food sources, like fishery byproducts that would have been thrown out anyway, algae, or soldier flies, for example, to make fish feed.

What's the problem with where fish farms are located?

This is a thornier issue. Any time you aggregate large amounts of livestock in an area, you're going to attract disease. In the case of salmon, the most famous disease is a parasite called a 

. When wild salmon swim past farms, the sea lice can infect them. If a juvenile salmon gets more than 10 sea lice, it will die.

The other issue is that if you have a lot of animals poop in one place, you can have nitrate overload, and cause algal blooms in the marine environment. So there are lots of people who would like to see fish farms taken out of the ocean entirely and moved to a tank.

The documentary goes through a lot of potential solutions. What do you think the most promising ones are?

The no-brainer is that we should eat more kelp and mussels, because they just filter water and get their nutrients without being fed. But of course not everybody likes mussels or kelp.

Farmed fish can be acceptable, if we're getting more protein out of it than we're losing to disease and fish feed. I'm not sure if anyone has run the numbers. The issue is that if consumers aren't aware of all of the options for farmed fish out there, they'll just go with what's cheapest. I did come across a farm in Norway where they were stocking fish less densely. To feed the fish, they were using offcuts of other fisheries, instead of directly harvested wild fish. And they were trying to address the sea lice problem with a fish called a 

 that eats the lice [instead of using medicine to kill them, which can kill some other forms of sea life like shrimp as well].

They are cute. There's an extended scene that got cut from the documentary where I kept trying to get a lumpsucker — [which has adhesive discs on its chest] — to stick to my forehead. I couldn't get it to.

You already knew a lot about fish when you started making this documentary. Is there anything you learned that surprised you?

One thing I learned is that about a third of wild salmon in Alaska start their lives in a hatchery. They're hatched [by 

private nonprofits and the Alaska Department of Fish and Game

] to boost the productivity of rivers. It's an issue that comes up because the salmon farming community competes with Alaskan fishers for consumers. When farmers get a lot of heat from the Alaskan wild fishing community, the farming community will say, "Hey, you're just ranching salmon. You're doing aquaculture, but you're not calling it aquaculture."

I knew a little bit about the hatcheries, but I'd never heard the Alaskan fisher's side of things. The fishers said that often these salmon are being introduced into inlands that never had salmon to begin with, so these salmon aren't competing with wild-born salmon, and really are supplementing the population.

Farmed vs. Wild Salmon Fishing in Alaska | The Fish on My Plate | FRONTLINE

Now let's switch to the more personal part of the documentary. You ditched land meat and ate fish every day for a year to see how the diet would affect your health. Specifically, you were interested in getting a higher level of omega-3s. What are omega-3s?

Omega-3 is a fatty acid, a long hydrocarbon chain with a double bond at the third spot from the end, which seems to make it particularly bendy and adaptable to serving multiple purposes in the cell. It is the Forrest Gump of molecules.

Whenever an important health issue comes up, so does omega-3. But we're never quite sure what it does. When people first started talking about it in the 70s, everyone got very excited because a study found a correlation between omega 3-s and low levels of heart disease. Since then, we've gotten statins, we've gotten angioplasty — all these ways of dealing with heart disease. So we're not as focused on how, if at all, omega-3s affect heart health anymore.

What we worry about now is dementia. So now everyone's obsessed with omega-3's neurological effects. And of course we're obsessed with our children and how smart they are, so we want them getting enough omega-3s. [

 for a study The Salt covered about the effect of omega-3s on brain functioning.]

What is it like to eat fish for a whole year? Did you get sick of it?

I got sick of it at the beginning, but then I broke through. Two things happened: First, once the meat section of the supermarket became a no-fly zone, instead of looking at fish as one of four options — chicken, beef, pork, or fish — I started to see fish as containing many options within its self-contained world. There was one that might be nice broiled, or another that might be nice with a sage sauce, and another that might be brought out by rosemary. It led me to a much more diverse approach to cooking fish.

The other thing that happened with eating fish all the time is that I lost weight. Now, there's a confounding factor: When you go to a restaurant, the fish always comes with the healthy stuff. If you order the steak, it comes with fries, but if you order the salmon, you get some nice steamed broccoli. So I don't necessarily contribute the weight loss to the fish but to leading me to healthier patterns of eating.

We'll let people watch the documentary to see how your health is affected by eating fish for a year. Given what you learned while making the film, what's your approach to eating fish going forward?

So, people will see in the film that I get some disturbing results regarding my mercury levels at the end of a year. [Large amounts of mercury 

released from coal-powered plants ends up in the oceans

 and eventually, in marine organisms, including fish.]

, so I can be a little cavalier with my mercury levels. But I've backed away from eating fish every day. I've probably backed down to three or four times per week, which is still double what the average American eats. And I try to eat more mussels.

I had a really intense embrace of the anchovy, particularly the Peruvian anchoveta, 90 percent of which is ground up and fed to pigs, chickens and farmed fish. But it's a really good source of protein and omega-3s.

When we went to Peru for the film, we went to a cannery in the south. They were so excited someone wanted to eat the fish as opposed to grind them up, that they gave me a 10-lb container of anchovies. I found anchovies are good in an omelet. And a piece of sourdough with free-range butter and anchovies: delicious.

Natalie Jacewicz is a science writer living in New York City.

Environmental News

Water

Natalie Jacewicz

Author

In order to investigate how eating fish affects our health as well as the oceans, author and fisherman Paul Greenberg spent a year eating fish every day.

Greenberg set out to answer "What fish is good for me and the planet?"

Courtesy of FRONTLINE

Norway, where modern fish farming was invented.

What fish is good for me and the planet?

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