Menus Subscribe Search

Follow us


Can Farmed Fish Flourish on a Veggie Diet?

• February 16, 2012 • 4:00 AM

It’s a fish-eat-fish world out there, which is bad news for ailing fisheries providing feedstock for aquaculture. If only some key dinner-table species were vegetarians, smaller fish would be spared.

Seafood reached a tipping point in 2009 when, for the first time, more than 50 percent of fish used for human consumption came from farms.

That might sound like good news for oceans, but farmed fish largely subsist on a steady diet of smaller fish, which are caught from fragile fisheries. It’s not a sustainable equation.

Aaron Watson, a researcher at University of Maryland’s Center for Environmental Science, says there is clear evidence that we are “fishing down the food chain, catching smaller and smaller fish to bring to the table and to bring to market, depleting wild populations and destroying natural habitat.”

Such small species, like sardines, anchovies, herring, and capelin, aren’t thrown whole to their penned cousins; they are ground into ground into fishmeal, or mashed into fish oil. There is a term used in aquaculture: fish-in fish-out, and it’s a rough measure of how many fish it takes to raise each fish that gets sold at the market. And in marine aquaculture it is generally agreed that a lot more fish go in than come out. In 2006, by conservative estimate, 16.5 million tons of fish captured from the wild went to feed farmed fish.

To control costs and extend supplies, fish farmers have tried stretching their resources, replacing increasingly expensive fishmeal with grain or soy protein. It works — to a point. There is a limit to how much one can water-down fish feed and still raise healthy stock.

“Right now most commercially produced diets for fish farms are generally 20 percent to 40 percent fish meal, and up to 30 percent fish oils,” Watson said. The meal provides the proteins, and the oil providing fish with the omega-3 fatty acids essential to their health.

Once a marine fish diet falls below about 20 percent fish meal, he says, “regardless of what protein source is used to replace the fish meal,” the fish start to show “reduced growth rates, reduced food intake, and reduced survival.”

Unlike their leaf nibbling freshwater cousins, the carps and tilapia, some of the best-tasting marine fish, such as tuna, salmon, and sea bass, are carnivores. In many cases, they are apex predators, and they can’t be convinced to eat more veggies.

Nevertheless, Watson decided to give it a shot.

Working with a carnivorous species of cobia in a University of Maryland lab, Watson provided his fish with a carefully planned vegetarian diet, combining proteins from soy, wheat, and corn gluten, with a mix of vitamins and supplements designed to provide all of their essential needs.

“We couldn’t get them to eat it,” he said.

Running down potential factors behind their finicky behavior, Watson considered the possibility that an amino acid deficiency might be involved. But which one?

When Watson added a small volume of taurine — an amino acid found only in meat and fish — to the same plant-based food the fish had rejected earlier, “they ate the feed like crazy, and they grew just as well, if not better, than the same species will grow on commercial diets using fishmeal.” (Watson’s results were published in the February issue of International Aquafeed.)

Without the supplement, Watson says, the vegetarian fish diet would have been nearly devoid of taurine. Although not considered essential for humans, who may nonetheless thrill to an occasional shot of taurine in a swig of Red Bull, predators, such as cats, require taurine in their diets.

In cats, taurine is essential for the development of the eyes – they go blind without it, and it plays a role in the digestive system in other animals as a component of bile acids.

Animals that can’t produce enough taurine to meet their needs can only obtain it by eating meat or fish. “A lot of these top predators and other carnivorous species are like cats,” Watson explains. “Their natural diets are composed solely of being carnivores and killing and eating other animals. A lot of the species we’re working with here have followed that same evolutionary path that cats did, so they also ended up with a taurine requirement.”

Because taurine is not incorporated into animal proteins, including fish proteins, it has generally not been regarded as essential, and Watson says that perception may explain why researchers may have overlooked its importance to fish in the past.

Getting the fish to eat their protein bars leaves one major dietary challenge on the path to vegetarianism: finding a replacement for fish oil as a source of the omega-3 fatty acids.

Professor Allen Place of the University of Maryland’s Institute of Marine and Environmental Technology says there are products made from algae that could fulfill that role, and he has successfully tested an omega-3 source derived from canola on fish in the lab. But he concedes these products currently cost more than fish oil, and getting farmed fish off their pelagic dependency is partly a question of economics. “If one could charge as little as a 10 percent premium for a completely fish oil-free, fish meal-free product, at an industrial level the economies of scale might make it work out,” he suggests.

And so far, it seems the newly converted vegetarian fish might make the grade at the table. Watson says taste testers from University of Maryland Seafood Quality Lab, in a double blind study, could not tell the difference between fish raised on standard fishmeal, and fish raised exclusively on his taurine-enhanced vegetable protein diet.

Sign up for the free Miller-McCune.com e-newsletter.

“Like” Miller-McCune on Facebook.

Follow Miller-McCune on Twitter.

Add Miller-McCune.com news to your site.

Subscribe to Miller-McCune

David Richardson
David Richardson began his journalism career operating a video news service in Washington, D.C., that covered federal agencies and Congress. His film production work has since ranged from postings at the White House to rural villages of Botswana, documenting community-centered HIV prevention programs. He holds a B.A. degree in government from Dartmouth College. He now writes on science, the environment and policy from Baltimore, Md., where he's had some success growing organic produce in a small backyard garden.

More From David Richardson

A weekly roundup of the best of Pacific Standard and PSmag.com, delivered straight to your inbox.

Recent Posts

October 22 • 4:00 PM

The Last Thing the Women’s Movement Needs Is a Heroic Male Takeover

Is the United Nations’ #HeForShe campaign helping feminism?


October 22 • 2:00 PM

Turning Public Education Into Private Profits

Baker Mitchell is a politically connected North Carolina businessman who celebrates the power of the free market. Every year, millions of public education dollars flow through Mitchell’s chain of four non-profit charter schools to for-profit companies he controls.


October 22 • 12:00 PM

Will the End of a Tax Loophole Kill Off Irish Business and Force Google and Apple to Pay Up?

U.S. technology giants have constructed international offices in Dublin in order to take advantage of favorable tax policies that are now changing. But Ireland might have enough other draws to keep them there even when costs climb.


October 22 • 10:00 AM

Veterans in the Ivory Tower

Why there aren’t enough veterans at America’s top schools—and what some people are trying to do to change that.


October 22 • 8:00 AM

Our Language Prejudices Don’t Make No Sense

We should embrace the fact that there’s no single recipe for English. Making fun of people for replacing “ask” with “aks,” or for frequently using double negatives just makes you look like the unsophisticated one.


October 22 • 7:04 AM

My Politicians Are Better Looking Than Yours

A new study finds we judge the cover by the book—or at least the party.


October 22 • 6:00 AM

How We Form Our Routines

Whether it’s a morning cup of coffee or a glass of warm milk before bed, we all have our habitual processions. The way they become engrained, though, varies from person to person.


October 22 • 4:00 AM

For Preschoolers, Spite and Smarts Go Together

New research from Germany finds greater cognitive skills are associated with more spiteful behavior in children.


October 21 • 4:00 PM

Why the Number of Reported Sexual Offenses Is Skyrocketing at Occidental College

When you make it easier to report assault, people will come forward.


October 21 • 2:00 PM

Private Donors Are Supplying Spy Gear to Cops Across the Country Without Any Oversight

There’s little public scrutiny when private donors pay to give police controversial technology and weapons. Sometimes, companies are donors to the same foundations that purchase their products for police.


October 21 • 12:00 PM

How Clever Do You Think Your Dog Is?

Maybe as smart as a four-year-old child?


October 21 • 10:00 AM

Converting the Climate Change Non-Believers

When hard science isn’t enough, what can be done?



October 21 • 8:00 AM

Education Policy Is Stuck in the Manufacturing Age

Refining our policies and teaching social and emotional skills will help us to generate sustained prosperity.


October 21 • 7:13 AM

That Cigarette Would Make a Great Water Filter

Clean out the ashtray, add some aluminum oxide, and you’ve (almost) got yourself a low-cost way to remove arsenic from drinking water.


October 21 • 6:00 AM

Fruits and Vegetables Are About to Enter a Flavor Renaissance

Chefs are teaming up with plant breeders to revitalize bland produce with robust flavors and exotic beauty—qualities long neglected by industrial agriculture.


October 21 • 4:00 AM

She’s Cheating on Him, You Can Tell Just by Watching Them

New research suggests telltale signs of infidelity emerge even in a three- to five-minute video.


October 21 • 2:00 AM

Cheating Demographic Doom: Pittsburgh Exceptionalism and Japan’s Surprising Economic Resilience

Don’t judge a metro or a nation-state by its population numbers.


October 20 • 4:00 PM

The Bird Hat Craze That Sparked a Preservation Movement

How a fashion statement at the turn of the 19th century led to the creation of the first Audubon societies.


October 20 • 2:00 PM

The Risk of Getting Killed by the Police If You Are White, and If You Are Black

An analysis of killings by police shows outsize risk for young black males.


October 20 • 12:00 PM

Love and Hate in Israel and Palestine

Psychologists find that parties to a conflict think they’re motivated by love while their enemies are motivated by hate.


October 20 • 11:00 AM

My Dog Comes First: The Importance of Pets to Homeless Youth

Dogs and cats have both advantages and disadvantages for street-involved youth.


October 20 • 10:00 AM

Homophobia Is Not a Thing of the Past

Despite growing support for LGBT rights and recent decisions from the Supreme Court regarding the legality of same-sex marriage, the battle for acceptance has not yet been decided.


October 20 • 8:00 AM

Big Boobs Matter Most

Medical mnemonics are often scandalous and sexist, but they help the student to both remember important facts and cope with challenging new experiences.


October 20 • 6:00 AM

When Disease Becomes Political: The Likely Electoral Fallout From Ebola

Will voters blame President Obama—and punish Democrats in the upcoming mid-term elections—for a climate of fear?


Follow us


My Politicians Are Better Looking Than Yours

A new study finds we judge the cover by the book—or at least the party.

That Cigarette Would Make a Great Water Filter

Clean out the ashtray, add some aluminum oxide, and you've (almost) got yourself a low-cost way to remove arsenic from drinking water.

Love and Hate in Israel and Palestine

Psychologists find that parties to a conflict think they're motivated by love while their enemies are motivated by hate.

How to Water a Farm in Sandy Ground

Physicists investigate how to grow food more efficiently in fine-grained soil.

Unlocking Consciousness

A study of vegetative patients closes in on the nature of consciousness.

The Big One

One company, Amazon, controls 67 percent of the e-book market in the United States—down from 90 percent five years ago. September/October 2014 new-big-one-5

Copyright © 2014 by Pacific Standard and The Miller-McCune Center for Research, Media, and Public Policy. All Rights Reserved.