Antimicrobial use in aquaculture: Some complementing facts

In their article “Global trends in antimicrobial use in food animals” (1), Van Boeckel et al. provide important insights into antimicrobial use in terrestrial animal production. Although aquaculture was deliberately excluded from their study, some extreme facts on antimicrobial use in aquaculture were mentioned. Here we briefly complement their study with more up-to-date information about the present use and trends of antimicrobials in global aquaculture.

Fish as food constitute 17% of global animal proteins, of which half originate from aquaculture (2). Aquaculture is a highly diverse activity involving more than 600 different freshwater and marine animal species farmed in a variety of production systems, compared with only around 20 species in terrestrial animal production systems (2). The aquaculture publications referred to by Van Boeckel et al. (1) describe antimicrobial use in Chilean salmon production in 2002 (Salmo salar) and giant tiger shrimp (Penaus monodon) production in Vietnam in 2003, two sectors that made up 24% of global Atlantic salmon production and 7% of global shrimp production in 2013. These two systems are rather extreme examples, as Chile uses 60 times more antimicrobials compared with the other three top salmon-producing countries combined (3), and only 3% of grow-out shrimp farmers in Vietnam were still using antibiotics in 2011/2012 (4). This shift is a result of stricter regulations in both producing and importing countries, vaccinations (which allowed the Norwegian salmon industry to reduce antimicrobial use by two orders-of-magnitude), biosecurity and better management, probiotics, and specific pathogen-free fry (4). Disease prevalence, and consequently therapeutant use, is also higher in the giant tiger shrimp compared with the whiteleg shrimp (Litopenaeus vannamei), the most commonly farmed shrimp worldwide.

Even though antimicrobial use in aquaculture still is a cause of concern, the aquaculture industry has changed its practices dramatically. Prophylactic treatments are today more rare (4), and the development of new vaccines, pre- and probiotic microorganisms, alongside better water management strategies promise further reductions in antimicrobial use. Moreover, even though antimicrobial classes and modes of application (most commonly with feeds) are similar for terrestrial and aquatic animals, the number of authorized compounds for livestock is larger than for aquaculture in developed countries (5). There are also large similarities between the resistance mechanisms shown by zoonotic pathogens affecting these two production sectors (5). Antimicrobial uptake efficiency and the manageability of the antimicrobial residues (i.e., water effluents compared with manure), however, differ with the magnitudes of discharges and their environmental pathways.

With an unarguably turbulent past and with reservations for still problematic sectors, aquaculture overall offers a source of animal proteins with relatively limited antimicrobial use. Aquaculture may, however, have larger environmental discharges and side-effects on aquatic ecosystems, whereas livestock has larger effects on soil biota. The industry should therefore continue to strive toward alternative and better practices. Aquaculture certification standards (e.g., Aquaculture Stewardship Council) also help to limit antimicrobial use, but regulations and institutional capacity following up on these are also important to cover small-scale farmers that may not be subject to certification.