Can farmed fish save aquaculture?

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This article first appeared on Ensia.

Eleven thousand years ago, the invention of agriculture made stable food supplies possible for the first time. In a relative blink of the eye, farming whisked aside 2 million years of hunting and gathering. 

Since then, agriculture has met ever-expanding demands for food with innovations such as selective breeding, draft animals, mechanization, hybrid seeds and artificial fertilizer. Progress continues to this day: In the United States, farmers raise 2.5 times as much food today as they did in 1950, and they’re doing it with no increase in costs of labor and inputs such as seeds, fertilizers and chemicals.

Impressive as that is, it may not be enough. Expected global population and demographic changes mean we need to double (or nearly double) our food production by the 2040s. But agriculture already uses 38 percent of the world’s land, and there’s no way to increase that meaningfully, much less double it, without massive deforestation. We need to do more with less, but how?

One solution is aquaculture, or fish farming. Among the oldest ways of producing food, aquaculture is also one of the most efficient — and, I contend, the best tool we have for feeding an estimated 9 billion people by the early 2040s. In terms of their environmental footprint (finprint ?), fish easily outcompete chicken, pork and beef. Here’s why.

Why cows can’t compete

Resource requirements for food animals depend on the amount of corn, soy and other crops we produce to feed them and how efficiently they use their feed. It takes about 2 pounds of feed to produce a pound of chicken, 4.5 pounds to raise a pound of a hog and 9 pounds for beef cattle.

But we don’t eat cows. We eat steaks and burgers, and only 40 percent of the weight of cattle at the farm ends up on a plate. Chicken and pigs do better. We eat 58 percent of a chicken (PDF) and 56 percent of a pig.

Fish have decided advantages over land animals. Because they live in a weightless environment, they spend less of their food energy making bones that we don’t eat and more making muscles that we do. That means we can eat more of a fish than we do with a land animal. And they’re cold-blooded so they don’t have to use part of the food we feed them to maintain their body temperature, as warm-blooded food animals do — boosting their feed-to-food conversation efficiency. By contrast, it takes about 1.3 pounds of feed to raise a pound of fish. And, with salmon, for instance, we eat 64 percent of the fish.

A thought experiment

Imagine that without changing the total amount of animal protein Americans eat, we shift the composition away from land animals to consumption of sea creatures by reducing annual consumption of chicken, pork and beef by 10 pounds each and increasing fish on our menus by 30 pounds per year.

Because fish production is so much more efficient than production of land animals, we could produce an additional 44 pounds of fish per capita for over a billion people without producing any more feed than we do currently.

There is a caveat here: Many farmed fish today are fed fish meal and fish oil that come from fish captured from wild fisheries, and harvests of those fish are at their sustainable limits. However, changes are at hand.

Fish meal provides protein for fish diets, but there’s no reason protein must come from fish meal. For instance, soy meal and even insect larvae (see here and here) substitute well for fish meal. Using them instead of fish meal helps break aquaculture’s dependence on marine ingredients.

With fish oil, the story is different. Fish oil provides aquaculture diets with required long-chain omega-3 fatty acids. In the ocean, plankton make long-chain omega-3 oils that travel through the food web, eventually ending up in the fish rendered to make fish oil. The aquaculture industry is devoting large efforts to find land-based ways to replace fish oil in aquaculture diets. Algae (see here and here), yeast and plants (see here and here) have been successfully developed as sources of essential omega-3 oils. As their production increases, they will provide alternatives to the fish oil-based omega-3 oils in fish diets.

Another thought experiment

On its 822 square miles, Duplin County, North Carolina, produces more hogs than any other county in the country, roughly 2 million per year (PDF). This adds up to 280 million pounds (PDF) of meat. To produce as much animal-derived food as Duplin’s hogs, what size fish farm must you build?

We’ll make our hypothetical farm 16.4 yards deep. Within it, fish never will exceed a density in their pens greater than 20 pounds per ton of water — a relatively low density in fish-farming terms.

Lastly, to be very conservative, let’s assume we eat only 50 percent of each fish we grow (the rest being fins, bones, intestines and other less palatable parts).

Our hypothetical farm fares well. To match the hog production on the 822 square miles of Duplin County, our fish farm requires a bit less than nine-tenths of a square mile on the ocean surface. And that’s just a microfraction of the ocean suited for fish farming.

The comparison is imperfect; not all of Duplin County is hog farms because air and water quality issues preclude increased production. In other words, Duplin County’s hog production has hit its upper limit; fish farming is far, far from doing the same.

Checking both boxes

Make more. Use less. Aquaculture checks both boxes — exactly what we know agriculture of the future must do.

We need more sustainably raised and nutritious food. Aquaculture clearly can provide it. And aquaculture is the fastest growing segment of agriculture. It is poised to contribute meaningfully to our future food needs.

Of course, aquaculture isn’t the single answer to our future food needs. There is no single answer to how we construct our future food supply. But aquaculture changes a very somber outlook to one that fairly oozes hopefulness.

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