Antimicrobial resistance: Can sustainable integrated multi-trophic aquaculture reduce AMR in aquatic systems
The global aquaculture industry has recently undertaken a dual approach to increase production while addressing criticisms towards the environmental impact of aquaculture production.
Integrated Multi-Trophic Aquaculture (IMTA) has been suggested as a production process that can reach this dual aim.
The IMTA aims at the integrated production of multiple aquaculture species of different trophic levels under a circular economy approach to improve efficiency, minimise energy losses, reduce waste and environmental deterioration and provide ecosystem services, such as bioremediation.
Bioremediation is a branch of biotechnology that uses living organisms, like microbes and bacteria, to remove contaminants from soil, water and other environments.
Species at the lower trophic level — usually plants or invertebrates — use waste products, such as faeces and uneaten feed from the higher trophic fish species, as nutrients.
The lower trophic species can then be harvested in addition to the fish to give the farmer more revenue, or even to be fed back to the fish.
It is suggested that IMTA systems are more efficient in mitigating diseases and preventing the spread of certain parasites.
As a result, IMTA may require lower doses of antibiotics and drugs, thereby potentially reducing the risk of antimicrobial resistance (AMR) in the direct environment of the farm.
The spread of diseases and parasites is found to be lower for IMTA systems, although it is highly dependent on species selection and environmental factors.
IMTA has been widely used to reduce aquaculture’s environmental pressure and increase profits. But the effects of IMTA on host immune and metabolic responses — the dynamics of bacterial communities and antibiotic resistance genes (ARG)— are relatively understudied.
A team of researchers in Southwestern Taiwan worked on an IMTA system established for farming milkfish (Chanos chanos). In this system, fish were cultured with organic extractive shellfish and inorganic extractive seaweeds.
They isolated 31 sulfonamide-resistant bacterial species and raised concern about the cross-transfer of antibiotic resistance from one pathogen to another.
Recently, another researcher studied the IMTA mariculture (cutivation of fish or other marine life for food) systems with different combinations of the hybrid grouper — the white-leg shrimp and the algae Gracilaria bailinae.
The results showed that the algae could effectively remove inorganic nutrients accumulated in water. This, in turn, significantly enhanced non-specific immunity and glycolipid metabolism in the hybrid grouper.
Several ARGs were documented throughout the culture process. But the relative abundance of these ARGs in three of the four culture systems decreased with culture time. This was especially the case in the monoculture and the fish-algal IMTA systems, indicating that these aquaculture systems had a scavenging effect on ARGs in the environment.
Approximately 25 bacterial groups of Bacteroidetes and Proteobacteria were significantly correlated with ARGs. The study also evaluated the IMTA system’s effects during the initial aquaculture stage.
Their study provided deep insights into further optimising culture methods and controlling ARGs’ spread and ecological risk in IMTA systems.
Developing sustainable and well-maintained IMTA systems could be a new hope to constrain AMR as IMTA systems aim to reduce the outbreaks of pathogens.
A sequential IMTA system should show the superior ability to maintain the prevalence of AMR and the integrity of the bacterial community structure compared to the traditional farming system, representing a potentially valuable aquaculture system.
Although the IMTA system maintains the prevalence of AMR, the ARGs will typically congregate from all the different trophic levels into a singular trophic level, which might be a potential problem.
The authors are with the Department of Aquatic Animal Health, Faculty of Fishery Sciences, West Bengal University of Animal and Fishery Sciences, Kolkata
Views expressed are the authors’ own and don’t necessarily reflect those of Down To Earth