Next up on our antimicrobial resistance (AMR) series: antimicrobials in aquaculture. Similar to livestock production, antimicrobials are used in fish farms to treat and prevent diseases, and are commonly administered via water medication and medicated feed. While these methods do encourage the development of AMR, they are not its only source—the use of organic fertilisers, such as farm animal wastes, also contribute toward AMR, especially if the waste was from livestock already extensively fed with antimicrobial agents (Aly and Albutt, 2014).
Aquaculture production has surpassed wild catch since 2012, with an average person now consuming almost double the amount of seafood compared to the past 50 years (Ritchie, 2019).
More crucially, while the use of antibiotics in aquaculture remains the same as their livestock counterpart, the dosage administered in the former can be much higher proportionally compared to the latter (O’Neill, 2015). This, combined with the fact that antibiotics can remain within the aquatic environment for an extended period of time—there is evidence to suggest that 70 to 80% of antibiotics fed to fish are excreted into the water (Cabello et al., 2013; Burridge et al., 2010)—has led to experts dubbing aquaculture sites as “reservoirs” and “hotspots” for AMR genes (Van et al., 2020; Watts et al., 2017; Muziasari et al., 2016).
The situation is further aggravated by the rapidly growing practice of aquaculture itself—since the stress of industrial-scale farming compromises the fish’s immune system, it justifies the widespread use of antibiotics as a way to compensate for the fish’s increased vulnerability to infections and diseases (Meek, Vyas, and Piddock, 2015). A recent study between CIRAD and French National Research Institute for Development has also shown global warming may even promote the use of antibiotics, particularly in the low- and middle-income countries—warmer temperatures almost always result in higher mortality rates of fish, which could lead to an increased use of antibiotics (Reverter et al., 2020).
Unsurprisingly, the development of AMR in aquaculture production (as with any other agri-food industries where antibiotics are used) adversely has devastating affects on the environment and public health, typically in the form of superbugs, i.e. bacteria that should have been killed by antibiotics, but instead evolved to become stronger. Yet, overall data on the amount of antibiotics used in aquaculture and how much of it is absorbed into the aquatic surroundings is still far from satisfactory. Approximately 90% of global aquaculture production is carried out in countries where regulations on antimicrobial use are either lax or non-existent, resulting in data that varies greatly from nation to nation (Watts et al., 2017).
The figure above depicts the global multi-antibiotic resistance (MAR) index calculated from aquaculture-derived bacteria. An MAR index of 0.2 indicates a high-risk of antibiotic contamination. The mean global MAR index is 0.25. 28 countries out of the 40 selected for study displayed an index of higher than 0.2 (Reverter et al., 2020).
Nonetheless, there is evidence to suggest that antibiotic use is dependant on a country’s regulations and legislation on the same. For example, in Chile, where there have been resistance from some aquaculture companies against the government’s attempts to regulate antibiotic use, approximately 300 tonnes of antibiotics is used every year in the aquaculture industry. As a comparison, Norway imposed stringent legislation on antibiotic use in aquaculture (and largely replaced with more sustainable alternatives such as vaccines) and now relies on only one tonne per annum (FAO, accessed June 2020).
There is some sliver of hope, however. Some companies are beginning to respond to the growing concern on the impacts of antibiotic use. Chilean-based Marine Harvest, one the largest marine farming enterprise in the world, has pledged to slash its antibiotic use from 450gm per metric tonne of harvested salmon to 150gm per metric tonne. Lerøy Seafood Group from Norway has stopped using antibiotics in their fish farms since 2017 (although it should be noted that as mentioned before, Norway as a whole had already enforced strict monitoring of the antibiotics use, which included measures such as a traceability system that tracks the health and harvesting details of fish products). Nevertheless, experts widely agree that much more needs to be done.
This is the third article of a multi-part series on the topic of antimicrobial use in the agri-food sector by Khor Reports. Read the previous posts here: Antimicrobial Resistance: Part #1 - The General Gist; Antimicrobial Resistance: Part #2 - Antimicrobials in Livestock.
In separate news, a newly found cluster of coronavirus cases from the Xinfadi meat market in Beijing recently triggered a consumer panic after traces of the virus were found on a chopping board used to cut up imported salmon. The discovery prompted China to temporarily stop salmon imports into the country as numerous eateries and supermarkets began pulling foreign fish and meat products from their menus and shelves.
In response to this incident, the Norwegian Food Safety Authority and Norwegian Seafood Council stressed that there are no cases of coronavirus infections spreading via contaminated food. This claim was later backed by the China Center for Disease Control and Prevention, who further clarified that there is currently no evidence to suggest that salmon itself could host the said virus.