Twenty years ago, when farmed salmon and shrimp spread in supermarket freezers, an influential scientific paper appeared warning of an environmental problem: fish farms devoured wild fish stocks, spread disease, and caused marine pollution.
This week, some of the same scientists who published this report released a new paper concluding that fish farming is much better, at least in many parts of the world. The most significant improvement is that farmed fish do not feed as much wild fish. They were fed more plants like soy.
In short, the paper found that farmed fish like salmon and trout had largely become vegetarians.
The latest study, which brings together hundreds of researches done in the global aquaculture industry over the past 20 years, was published in Nature on Wednesday.
The results have real implications for nutrition, employment and biodiversity. Aquaculture is a source of income for millions of small-scale fishermen and a source of income for fish-exporting countries. It is also important if the 7.75 billion people of the world are to continue to eat fish and shellfish without draining the ocean’s wild fish stocks and marine biodiversity.
At the same time, there have long been concerns among some environmentalists about the effects of aquaculture on natural habitats.
The new paper found promising developments, but also persistent problems. And it didn’t quite inform the average Pisces Easter of what to eat more of or avoid.
The aquaculture industry is too diverse to be broadly generalized, said Rosamund Naylor, professor of Earth System Science at Stanford University and lead author of the 2001 warning paper and overview released on Wednesday.
“The aquaculture industry is so diverse (over 425 species grown in all types of freshwater, brackish water and marine systems) that it makes no sense to classify them all into a ‘sustainable’ or ‘unsustainable’ category.” Dr . Said Naylor in an email. “It has the potential to be sustainable. So how can we make sure it moves in that direction?”
Global aquaculture production has more than tripled in the last 20 years, producing 112 million tonnes in 2017, the last year for which statistics are cited in the publication. China is a leader and produces more than half of all farmed fish and shellfish worldwide. Outside of China, Norway and Chile are big players producing farmed Atlantic salmon, while Egypt produces the Nile tilapia. Most of the fish produced in Asia is consumed in Asia, which means that it serves as an important source of protein for the citizens of these countries.
The study also found that the production of farmed algae and mussels such as oysters and clams had also increased dramatically. This is perhaps the most encouraging news, as neither seaweed nor clams need additional food to reproduce. They filter nutrients from the water and in turn produce food for human consumption.
The study also found that freshwater aquaculture now accounts for 75 percent of all aquatic agriculture. The most noticeable result, however, was the change in fish feed, especially in carnivorous fish such as salmon, which were traditionally fed on many wild fish such as anchovies. The study found that farmed fish production tripled between 2000 and 2017, although catches of wild fish, which are used to make fish feed and fish oil, decreased.
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Martin Smith, an environmental economist at Duke University who was not involved in the study, said the changes in aquaculture were partly due to new regulations in some countries – rules in Norway, for example, reduced the spread of sea lice on salmon farms – but mostly because the aquaculture industry had no reason to buy expensive wild fish feed once it could develop plant-based alternatives.
“It has always been in the interests of aquaculture to reduce its most expensive ingredient,” said Dr. Smith, who took a class called “Should I Eat Fish?” Informed.
“The language around aquaculture was too negative and too pessimistic,” he said. “But the industry has also gotten much better.”
However, the authors of the most recent study suggest that the problems persist.
Aquaculture needs better monitoring to ensure that environmentally sound practices are followed and rewarded. “However, many aquaculture systems are still not motivated to meet sustainability criteria,” the authors state, “because their target markets do not reward producers with improved prices or better access.”
Some countries need to better manage the use of antimicrobials in fish ponds to protect themselves from drug-resistant microbes. Aquaculture continues to be vulnerable to extreme climate events and disruptions in world trade, such as those caused by the coronavirus pandemic. And then the question arises, where does the soy used for fish farming come from? The aquaculture industry is under increasing pressure to make sure it does not source soy from deforested areas like the Amazon.
“As with all food systems, consumers need to realize that there is no such thing as free lunch, but there are important decisions that can be made with sufficient information,” said Dr. Naylor.
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