Aquaculture Threatened on All Sides

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As the global population grows, most dramatically in low- and middle-income countries, many are looking to aquaculture to meet the growing demand for protein. Some studies project that this demand will drive global aquaculture to increase by 62% by 2030. However, aquaculture faces the double threat of antimicrobial resistance and elevated temperatures. As aquaculture production intensifies to meet growing demand and global temperatures rise, these threats will only increase. These problems call for stronger regulations of antimicrobial use in the short term. In the long term, it may be best to look to more stable and sustainable plant protein sources to feed the world.

In aquaculture, as inland animal agriculture, antibiotics are used both to treat disease and to speed up growth. However, as seen in human clinical settings, overuse of antimicrobial treatments kills off weaker strains of pathogens, leaving stronger, antimicrobial-resistant strains to thrive with little competition. These resistant strains can then decimate entire populations of aquatic animals unchallenged. 

In a meta-analysis of 460 articles, researchers explored the relationship between multi-antibiotic resistance (MAR) in aquaculture and temperature, climate change vulnerability, and human clinical MAR for 40 countries, which together account for 93% of global aquaculture. They found that aquaculture MAR is strongly correlated with human clinical MAR, climate change vulnerability, and average annual temperature. They also found that these three threats converge primarily in low- and middle-income countries, which tend to be the most food insecure, meaning that aquaculture MAR could translate quickly to widespread malnutrition if these populations come to rely heavily on aquaculture.

The analysis also showed that fish infected with various diseases die at higher rates as temperatures rise. Every 1°C increase in water temperature translates to a 3-6% increase in diseased fish mortality. This means that as global temperatures climb, aquaculture is threatened not only by MAR, but by increasing mortality from common diseases. These two threats dovetail in countries with both high aquaculture MAR and high annual temperature. The average annual temperature in a given country explains 9.1% of aquaculture MAR. We see this convergence primarily in low- and middle-income countries, which also tend to be highly vulnerable (climatically and economically) to climate change.

Based on their findings, the researchers call for stronger regulatory controls on antimicrobial use in aquaculture and animal agriculture and in human clinical settings. These metrics are highly correlated and likely mutually reinforcing: Effluent from human and animal agriculture sources contaminates nearby bodies of water, impacting aquaculture, and pathogens from aquaculture can find their way into the water sources used by nearby people and land animals. Human clinical MAR explains 17.9% of aquaculture MAR, and resistant microbes from aquaculture, in turn, threaten humans directly and through decreased food supply. The researchers also see a need for better sanitation systems to control the spread of resistant microbes. They recommend that aquaculture disease be managed through vaccination, food supplements, and improvement of ecosystem resilience rather than through the overuse of antimicrobials.

These steps may indeed help stave off the collapse of aquaculture systems. However, there is real danger in relying on this increasingly emperiled industry to meet the world’s protein demand. The aquaculture industry, with its reliance on antimicrobials that are increasingly useless against resistant pathogens and its susceptibility to rising temperatures, is too fragile to be depended upon. Instead of teaching the world to farm fish, perhaps we should be teaching the world to grow vastly more sustainable protein-rich plants that can safely and reliably nourish us all.