A 20-year retrospective review of global aquaculture

Naylor RL, Hardy RW, Buschmann AH, Bush SR, Cao L, Klinger DH, et al. A 20-year retrospective review of global aquaculture. Nature. 2021 2021/03/01;591(7851):551-63. 

Relevant to: 

All Dietitians-Nutritionists.  

Question: 

The authors provide an overview of the changes in global aquaculture from 1997 to 2017 through a review of relevant literature. Aquaculture refers to the practice of breeding, growing, and harvesting fish, shellfish, and aquatic plants. 

Bottom line for nutrition practice: 

As consumption of seafood rises worldwide, there has been tremendous growth in the aquaculture sector, with production tripling over the last 20 years. Asia is the largest aquaculture producer. While aquaculture was once thought of as a marine based activity, freshwater aquaculture now accounts for 75% of the world’s edible volume of raised seafood. Aquaculture has become integrated into the global food system, and is now linked to the land (e.g., fish can be raised inland, and some fish feed is grown inland). The number of species farmed has increased in the last 20 years, although fish, shellfish, and algae make up the majority of the volume. In addition to food, aquaculture generates a variety of other uses (e.g., industrial products, pharmaceuticals), and contributes to rural livelihoods and food security. Most farmed freshwater fish is consumed in domestic markets.   

One of the critiques in the past was the high use of wild fish included in farmed fish feed. An increased use of land based alternative feeds have decreased the amount of wild fish used in feed. The authors also highlight the unrealized potential of species such as seaweed and molluscs (e.g., mussels); these species may also be particularly helpful in providing ecosystem services, as they do not rely on external feed, and improve water quality. The sector will continue to face concerns and uncertainties such as PPP (pathogens, parasites, and pests), climate change and market disruptions (see “Details of Results” for more).   

The authors state that aquaculture systems can be designed and implemented to be sustainable.  

Moving forward, technology and governance will play important roles. Future initiatives to advance aquaculture need to balance nutrition, equity, justice, and environmental outcomes and trade-offs – both on land and at sea.  

Abstract:

The sustainability of aquaculture has been debated intensely since 2000, when a review on the net contribution of aquaculture to world fish supplies was published in Nature. This paper reviews the developments in global aquaculture from 1997 to 2017, incorporating all industry sub-sectors and highlighting the integration of aquaculture in the global food system. Inland aquaculture—especially in Asia—has contributed the most to global production volumes and food security. Major gains have also occurred in aquaculture feed efficiency and fish nutrition, lowering the fish-in–fish-out ratio for all fed species, although the dependence on marine ingredients persists and reliance on terrestrial ingredients has increased. The culture of both molluscs and seaweed is increasingly recognized for its ecosystem services; however, the quantification, valuation, and market development of these services remain rare. The potential for molluscs and seaweed to support global nutritional security is underexploited. Management of pathogens, parasites, and pests remains a sustainability challenge industry-wide, and the effects of climate change on aquaculture remain uncertain and difficult to validate. Pressure on the aquaculture industry to embrace comprehensive sustainability measures during this 20-year period have improved the governance, technology, siting, and management in many cases. 

Details of results: 

This paper follows up on a seminal paper on aquaculture published in 2000 by some of the same authors in Nature. Aquaculture has made many transformations in feed ingredients, production technologies, farm management and value chains over the last 20 years. Consumers in low to high income nations have gained from the year round availability of these nutritious foods. Most freshwater fish farming occurs in household-managed ponds and small- to medium-scale commercial enterprises within polyculture systems, and the products are consumed by domestic markets. As such, the authors suggest that little incentive occurs to participate in recognized/ certified sustainable practices. Aquaculture in Asia is very diverse, while industry in the Western Hemisphere relies mostly on single or dual production systems (e.g., Atlantic salmon in cages). Advances in feed technology and breeding have focused on the latter. Growth rates are increasing rapidly in South America and Africa. Alleviation of rural poverty seen in South and Southeast Asia through the development of aquaculture is now occurring in parts of sub-Saharan Africa.   

Plant based feed has increased in aquaculture, reducing the dependence on feed made from wild fish. Some Asian countries, however, still rely on feed-grade fish, which can impact both freshwater and marine ecosystems . Shifting feed to plant based is not simple, as carnivorous fish can have difficulty digesting carbohydrates and fish are more sensitive than livestock to antinutrients and toxins in plant proteins – thus increasing the risk of disease. Using land based crops for aquafeed leads to another set of trade-offs, as according to life cycle analyses, greater than 90% of the environmental impact from fed aquaculture production comes from feed. Single-cell proteins, insect meal, and microalgae are being investigated for replacement in feed.  

As outlined above under “bottom line”, while molluscs, and seaweeds have sustainable characteristics, they also absorb viruses, bacteria, toxic algae, and polluted organic particles, creating food safety risks when raised in polluted environments. Globally, more than 97% of the volume of aquatic plants and algae comes from aquaculture. Global production has tripled in the last 20 years, with most produced in Asia. Approximately 1/3 is consumed directly as food, while the rest is used by the food industry sector (e.g., additives and ingredients) and by the non food sector (e.g., pharmaceutical, feed ingredients, biofuels, bioplastics).  

Some environmental performance trends have been positive, such as the decrease in habitat destruction in mangrove ecosystems from shrimp farming. However, the authors detail many remaining challenges including the effects of pathogens, parasites, and pests (PPP), pollution, harmful algal blooms, and climate change. Over-intensification, particularly in cage aquaculture, has resulted in nutrient pollution and pathogen-related problems. The authors argue that investments are required in strategies to prevent PPP, and warn that as aquaculture expands – particularly in low income regions -PPP out-breaks and human health risks from chemical substances used to prevent and treat pathogens  

will occur. Mostly as a result of human activity, harmful algae blooms are increasing across the world in “frequency, magnitude, duration, geographical ranges, and species composition” (p.558). Decreased agricultural productivity and livelihoods occur as a result of climate change issues such as “suboptimal growing temperatures, sea-level rise (saltwater intrusion), infrastructure damage, droughts and freshwater shortages, and rising feed costs… [and] ocean acidification” (p.558).  
 
Given the diversity of aquaculture systems across the globe, a variety of strategies are required to advance sustainable production, including ecosystem-based management, system design, and new forms of private and public sector governance. The authors suggest that new technologies need innovative financial and environmental management in order to be successful. They further stress the need for flexibility in governance in order to support the diversity of the stakeholders, while remaining accountable to environmental and social performance.  

Of additional interest: 

Table (formerly FCRN), offers a “Ask the Author” review and question and answer recording of this review.  See: https://m.youtube.com/watch?v=YQx8a5n91X4&feature=youtu.be 

Editor’s comment:  

N/A 

Open access link to article: 

https://www.nature.com/articles/s41586-021-03308-6 

 Conflict of interest/ Funding:  

“R.L.N. is a member of the Forest Protection Advisory Panel at Cargill, and the Center on Food Security and the Environment (FSE) has received funding from the Cargill Foundation for visiting scholars and staff support (but not for research). There has been no overlap between Cargill and research activities relating to aquaculture at the FSE.” (p. 563)  

External relevant links:  

N/A

Corresponding author: 

roz@stanford.edu  
(Dr. Rosamond Naylor)  

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