Aquaculture now supplies 50 percent of the world’s fish
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The ever-growing demand for fish and fish oil due to their omega-3 fatty acids has led to exponential growth in the aquaculture industry—and depletion of the world’s oceans. While aquaculture is farmed fish, the fish are fed with wild marine species.
In a paper published in the Proceedings of the National Academy of Sciences researchers announced that from 1995 to 2007 global production of farmed fish nearly tripled. This year the industry is set to reach a new landmark: aquaculture will account for 50 percent of the fish consumed globally.
“The huge expansion is being driven by demand,” said lead author Rosamond L. Naylor, a professor of environmental Earth system science at Stanford University and director of the Stanford Program on Food Security and the Environment. “As long as we are a health-conscious population trying to get our most healthy oils from fish, we are going to be demanding more of aquaculture and putting a lot of pressure on marine fisheries to meet that need.”
 These are moi, or Pacific threadfin, being sorted for market after harvest from an offshore aquaculture cage in Hawaii. Credit: NOAA. |
Wild species that are not in great demand commercially, such as anchoveta and sardines, are ground up into fishmeal and fish oil and then fed in massive quantities to farmed fish.
“It can take up to 5 pounds of wild fish to produce 1 pound of salmon, and we eat a lot of salmon,” said Naylor.
The authors recommend lowering the amount of fish oil fed to farmed fish, pointing out that even a small reduction could have a big impact on lessening pressure on marine species: a reduction in oil of 4 percent would mean the amount of wild fish feed needed to produce one pound of salmon would drop from 5 pounds to 3.9 pounds.
“Reducing the amount of fish oil in the salmon’s diet definitely gets you a lot more bang for the buck than reducing the amount of fishmeal,” Naylor said. “Our thirst for long-chain omega-3 oils will continue to put a lot of strain on marine ecosystems, unless we develop commercially viable alternatives soon.”
In the near future there may be substitutes for wild caught fishmeal. Possibilities include protein from grain and livestock byproducts, omega-3 oils extracted from single-cell microorganisms, and genetically modified land plants.
However, a quicker change would be for consumers to switch from eating carnivorous fish—salmon, trout, tuna, etc.—which require large amounts of wild fish for food to herbivorous fish, such as Chinese carp and tilapia. Yet, the authors point out, even this is not so simple. While these ‘vegetarian’ fish could be fed solely with plant-based feed, the industry has been feeding even the herbivorous species wild fish-feed.
“Our assumption about farmed tilapia and carp being environmentally friendly turns out to be wrong in aggregate, because the sheer volume is driving up the demand,” Naylor said. “Even the small amounts of fishmeal used to raise vegetarian fish add up to a lot on a global scale.”
The authors recommended changes in the industry so that herbivorous fish would be fed only plant-based foods. In addition, they urge policy makers to look at regulating the industry before wild fisheries suffer a complete collapse.
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