THEGREENGROK    Planetary Watch

You Are What Your Farmed Fish Eat

by Bill Chameides | September 14th, 2009
posted by Erica Rowell (Editor)

Permalink | 1 comment


Fish farming presents many challenges. While there have been improvements to some of the practices, we have a ways to go for a more complete fix.

You can take the fish out of the ocean and raise them in a farm, but you don’t necessarily get the ocean’s protein from the farmed fish.

Harvesting ocean treasures is serious business. Today, some two billion people are critically dependent upon the ocean for protein. Many others look to the seas to supply a healthy diet rich in omega-3 oils. As a result, the demand for fish has been growing for decades. So fast that it appears to be outpacing the ability of the ocean’s fisheries to keep pace. Data show that fish populations are shrinking — both in terms of numbers and the physical size of the fish themselves. Many believe the current harvesting of the ocean is unsustainable.

The Problems With Farming Fish

What’s a hungry world to do? Why not fish farms? Instead of trolling the oceans for dwindling populations of fish, simply raise fish in ponds or pens and then harvest them on the farm. Problem solved, right? As a new paper by Stanford University’s Roz Naylor in the Proceedings of the National Academy of Sciences makes abundantly clear, the problem is definitely not solved.

First of all, pollution and water quality issues abound; then there’s the problem of disease spreading from farm to wild populations (see here and here); also, there are often toxins and contamination associated with farm-raised fish. But let’s not focus on those here — let’s just examine the ocean sustainability issue.

If you’re a fish farmer, you gotta feed your fish, the standard practice for which is fishmeal (and fish oil). That’s reasonable, fishmeal for fish.

But where does fishmeal come from? From fish in the ocean — usually so-called forage fish such as sardines, menhaden, and herring. You might think that because we humans generally do not eat forage fish, their use for fishmeal should pose no problem. But it does, because forage fish are an important link in the food web that supports the fish we do eat — think salmon and tuna. Overharvesting forage fish for fishmeal helps effectively overharvest our seafood because indirectly consuming more of the fish they eat means they have less food available.

Naylor and her colleagues have published some salient findings:

  • The amount of fishmeal fed to farmed fish has increased by more than a factor of two since 1995.
  • Between 20 and 30 million metric tons of fish are caught annually; of that, five to seven million metric tons go to fishmeal (and a smaller amount of fish oil). Almost 70 percent of this fishmeal is fed to farmed fish. (Put differently, farmed fish eat about 25 percent of the global fish catch in the form of fishmeal and fish oil.)
  • About another seven million metric tons of low-value fish is also caught and fed to farmed fish in other feeds.
  • Peru and Chile are the world’s biggest producers of fishmeal (about 40 percent of the world total).
  • Asian countries (especially China) are the world’s largest consumers of fish at a little less than 60 percent of the total.
  • Europe is the dominant user of fish oil (derived from ocean fish) to support its salmon farming. (By the way in case you didn’t know, virtually all Atlantic salmon you buy is farmed. Atlantic salmon are an endangered species.)

The Silver Lining: The Fish-in-to-Fish-Out Ratio in Fishmeal Is Declining

That’s the bad news, but there is a silver lining in the Naylor et al. paper. The amount of fishmeal being used to raise an individual famed fish is declining. The “fish-in-to-fish-out” ratio (FI/FO) of wild fish inputs to farmed fish outputs has been declining over the past decade: from an overall ratio of a little more than 1.0 in 1995 to about 0.6 in 2007.

That decline is being fueled in part by a growing demand for “sustainable fish.” Naylor’s team reports that the National Organic Standards Board “recently proposed limiting the use of fishmeal and fish oil in organically certified aquaculture products,” and bills limiting the amount of fishmeal in the feed for farmed fish are under consideration. (Just FYI: Lots of enviro groups oppose these bills for other reasons, mainly open ocean farming.)

Even more encouraging, Naylor et al. report that new technologies and products are being developed that would allow even lower dependence of fishmeal for farmed fish. These include the:

  • development of single-cell microbes that could supply necessary proteins and oils and
  • use of seafood by-products that would otherwise find their way to the wastebin.

Then there’s the potential boon that Naylor et al. found: an incredible 25–30 million metric tons of the global fish catch are lost to bycatch and processing byproducts each year — wasted fish protein that could offset the total amount of forage fish harvested annually for fishmeal.

But Before We Get Too Giddy About the State of Fish Farms …

Lest we prematurely celebrate the arrival of the sustainable fish farm, a few caveats:

  1. Because of the need for high-quality oils to grow salmon — which are prized by consumers because of their high omega-3 oil content — farmed salmon require high amounts of fishmeal. The average FI/FO for salmon is five! In other words, when we chow down on a salmon fillet, we’re really chowing down on the equivalent of five fish.
  2. The decrease in the FI/FO on many fish farms has been made possible by substituting grains (like barley, corn, and soybeans) for fishmeal — a substitution that raises a whole host of other problems. (See previous posts here, here and here.)
  3. Using bycatch to feed farmed fish is probably not such a great idea, as doing so might encourage bycatch, which in some cases is driving some species toward extinction.
  4. Even though the FI/FO has been declining, don’t forget that the total amount of fish we pull out of the ocean each year to feed the fish on the farm is still on the rise.

So, you want to eat sustainable fish from the farm? Caveat emptor.

filed under: faculty, food, oceans, overfishing, Planetary Watch, science, waste
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1 Comment

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  1. paulm
    Sep 16, 2009

    This is probably also true of Climate Change reform for the states… Michael Pollan Says Healthcare Reform Will Fail Unless We Change The Way We Eat

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