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[Editor’s Note: Questions have been raised about the validity of this study due to the ties of a least one of the authors to Cargill and the aquaculture industry. We will be keeping our summary of the study published, but readers should take note of this issue and read the findings below critically with this context in mind.]

In 2000, a research team raised the alarm about the use of wild-caught fishes as feedstock for captive-bred fishes. They warned that if aquaculture is to continue making a net positive contribution to the world food supply, then it would have to move away from using fish meal and fish oil (FMFO) from wild-caught fishes to make feed for captive populations. They’d also need to address other sustainability issues such as reappropriation of ecosystems and coastline degradation. 

Now, they look back at the last 20 years and reflect on how the industry has evolved and where it now stands in terms of sustainability and its contribution to the world food system. 

Opening the paper, the authors remark on the continued rapid expansion of the industry, in terms of both scale and diversity. With this comes an increased use of FMFO from wild-caught fishes. A greater proportion of farmed finfish are now fed, which may put excess pressure on the supply of FMFO. Another key observation is that the potential to utilize filter-feeding species, like mollusks and seaweeds, to improve environmental outcomes as well as provide economic benefits, is still underexploited. 

In the nearly two decades from 2000 to 2017, the global volume of production from aquaculture approximately tripled —from 34 to 112 million metric tons (Mt). Despite its huge species diversity, 75% of production was made up of seaweeds, carps, bivalves, tilapia, and catfish in 2017. China has been the biggest player in the industry since the turn of the century, farming the greatest quantity and diversity of species and also using the largest variety of culture systems and techniques.

This review focuses on the growth of freshwater aquaculture, which is simply the farming of freshwater species like tilapia, carp, and catfish. Freshwater aquaculture has been historically underrepresented in the scientific literature, perhaps because it consists mainly of household ponds for subsistence and small-medium enterprises for local and regional consumption. Here again, China dominates in global production, contributing 56% of global output, with all of Asia accounting for 93%. 

A major aspect of the 2000 review was the concern about the industry’s rampant use of FMFO from wild fisheries in intensive farms, especially at a time where wild fishery catches had plateaued. So how has the industry responded to this issue, and how has its use of this resource changed in the last two decades?

Despite the global production of fed fish tripling in the period, the annual catch of fishes used for FMFO has decreased from 23-16Mt, reflecting the industry’s increased efficiency with the use of FMFO. Some major drivers of this trend include:

• Rapid growth in the production of omnivorous species, who require less FMFO in their feed
• Improved feed conversion ratios, meaning that a captive fish today needs to eat less feed to put on the same amount of weight.
• Increased use of plant-based alternatives for proteins and oils in formulated feed
• Fish meal production technology has improved the extraction of fish meal. The use of trimmings from fish used for consumption to make fish meal has also increased, reducing reliance on forage fish landings. 

The doubling of the price of fish meal throughout the 2000s and the relative affordability of plant-based alternatives is undoubtedly a core motivator for these innovations. So despite aquaculture still being by far the world’s largest consumer of FMFO, the sector has definitely made improvements in its trends and trajectory here. 

Part of the industry’s move toward land-based (from terrestrial plants and animals) feed sources has been facilitated by the development of feed ingredients and formulations tailored for fish nutrition. Unfortunately, this has created a phenomenon whereby replacing the dietary fish content of piscivorous species with land-based feed alters gut, immune, and endocrine function. All this makes captive individuals more prone to disease.

Another major focus of this paper was the potential for extractive species like seaweeds, algae, and filter-feeding mollusks to improve the environmental performance of the aquaculture sector while also providing economic benefit and food security. Most bivalves don’t require feed inputs, making them an ideal choice for sustainable aquaculture expansion. Still though, despite considerable growth in China, mollusk farming grew at a slower annual rate than farmed fishes in the period, at 3.5% vs 5.7%, respectively.

Mollusks also fit into the industry in other ways. Outputs from mollusk farming can be used in pharmaceuticals, building materials, and fertilizers, not to mention the sequestration of nutrients like nitrogen and phosphorus, and shoreline stabilization mollusks can provide. They may also have detrimental effects on deep-water ecosystems by restricting the supply of phytoplankton and increasing disease risk. 

A similar story has played out for algae and seaweeds, who have seen increasing attention since the turn of the century for their use as not just a food source, but also for nutritional enhancement, other non-food uses, and ecosystem services. Global production tripled to 32Mt in 2017, and most was used in the food industry for functional food ingredients. A small amount was used for fertilizer, animal feed, cosmetics, pharmaceuticals, biofuels, and bioplastics. There is great potential for seaweeds to replace animals as a food source for humans owing to their unique nutritional profile. With research, innovation, and optimization, aquatic plants may replace many animals in the global food system in the future.  

Among the most persistent challenges faced by aquaculture are pathogens, pests, and parasites (PPP), as well as harmful algal blooms and effects from climate change. PPP has become a particularly damaging problem since the 2000s as a result of more and more extremely high-density farms, which catalyze the development and spreading of disease. For the most commonly produced and traded species, there have been considerable improvements in technology to identify and manage PPP in the last 20 years, but access to these technologies isn’t available to all producers due to prohibitive costs. 

Therapeutants (chemicals used to manage PPP, like antimicrobials) have become commonplace in the industry, but their use poses serious risks to the immediate and long-term health of both the captive and wild populations, as well as humans. Vaccines provide some hope of more robust solutions to PPP dangers, but have seen little use outside of high-value species like salmon and trout. Vaccines have the potential to tremendously reduce therapeutic use, but they’re also expensive and not easily standardized. Right now, best management practices are the most effective way to mitigate PPP risks.

Meanwhile, harmful algal blooms (HABs) have increased in frequency, duration, and intensity in the last two decades, largely as a result of human factors like wastewater runoff from farms. HABs can cause enormous economic losses, for example in Chile in 2016, HABs caused US$800 million in losses and two years of facility closures in salmon, mussel, and abalone farms due to food safety risks and mass-deaths. All this happening in the background of climate change makes predictions about the future of PPP and HABs quite uncertain. 

Technologies have been developed in recent years to address such challenges. Recirculating systems treat and reuse water, thus insulating against PPP and HAB risk, integrated multi-trophic systems use synergistic organism interactions to improve environmental outcomes, and offshore aquaculture takes place in deep, open waters to prevent damage to coastal ecosystems and to dilute wastes in order to reduce their potential to damage the surrounding environment. But no single system is without its disadvantages. 

So when we look back at the last 20 years of the industry, we see a trend towards better environmental performance and more efficient resource use as well as ongoing innovation in response to the challenges facing the industry. These trends seem to stem from necessity as the FMFO crisis has persisted and pestilence can still cripple production. We also see the potential for using algae, seaweeds, and bivalves to improve food security and environmental outcomes — if one can set aside the ethics of using bivalves. Perhaps the economic incentives and governance structures that currently exist aren’t yet enough to compel large financial and technological investments in this space. For animal advocates, the paper gives a thorough overview of the growth of the industry, and offers insight into possible leverage points for making change.