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  • Writer's pictureDirk

Not every solution is chemical

Updated: Dec 14, 2019

Toulouse/Berlin/Aberdeen. The increasing world population needs to be fed. The so far most widespread solution is application of chemical treatment, that inhibit pests and thereby boost yield of agriculture and aquaculture. Ideally, a pesticide should be fatal to the pests concerned only, and not to other non-target species in the vicinity, including humans and wildlife. Unfortunately, this is often not the case and triggered a controversy over the years weighing up the advantages on the use vs. the misuse of pesticides. The rampant use of these chemicals under the slogan "If little is good, much more will be better" has devastating consequences for human and other life forms. We need to find a way back to the more biological options to cultivate and to modernize farming, especially as (hopefully) more and more harmful chemicals will be banned in the future. We have to go back to nature to find solutions, for instance apply our ecological understanding to mitigate diseases. Researchers from Toulouse, Berlin, and Aberdeen have now provided an overview of biological means to fight fungal pathogens in aquaculture in the scientific journal Trends in Parasitology. They outline seven biological concepts to control fungal pathogens and show that biological treatments are possible and need to be developed further to limit further release of chemicals into the environment.

Aquaculture of fish and algae provides food to millions of people around the world. Those culturing approaches have mainly relied on the use of chemicals as treatment against pathogens and the diseases they cause. “We see an immediate result when we use chemicals, and that gives the impression that the treatment has been successful” says Prof. Dr. Dirk Schmeller from the Ecole Nationale Supérieure Agronomique de Toulouse (ENSAT). “We, however, forget the side effects of those chemicals, which can not only negatively affect the cultured species, but also the environment and humans that live there or consume the cultured plants and animals”, he adds. Some of the applied chemicals have now been banned by transnational regulations, as e.g. malachite green, and in general chemical treatment may be effective only in the short-term as resistances of pathogens to the treatment can evolve fast. “We have distanced ourselves from nature too far, while we can learn a lot from it” states Prof. Schmeller. He has led a team discovering that zooplankton, tiny microscopic organisms living in the water of lakes, can effectively eat spores of fungal pathogens. A biological control based on the idea that parasites and pathogens can be food for other organisms looks astonishingly simple, but has not found entry to aqua-culturing yet. Other biological means to prevent diseases are the control of biological vectors of pathogens so that they cannot enter into aquaculture, where it may spread quickly as a result of high-density growth of single species. These monocultures in general, while highly productive, are prone to succumb to pathogen infections quickly. “We have to start applying our ecological understanding of these organisms to limit spread of infections” specifies Thijs Frenken, the lead author of the report. It is wise to learn again how to culture multiple species in the same culture as an increased host diversity is much less susceptible to pathogens as is a monoculture. Immunization and vaccination, as well as the induced production of anti-pathogenic proteins are additional biological means to control pathogens in aquaculture. Here, natural defense mechanisms are triggered by simulating a fake threat to fool the culture species into excreting proteins that hamper pathogen growth or even kill the pathogen.

A relatively new field is that of probiotics, microorganismal communities that are claimed to provide health benefits. In aquaculture, e.g. natural bacterial communities could be used as antagonists/enemies to other fish-harming bacteria (e.g. Pseudomonas, Aeromonas). While probiotics appear to be a powerful tool for treatment, little studies have yet focused on adverse effects. “There is not one single perfect biological strategy for controlling aquaculture, but we are positive that with little extra effort a combination of them will be successful in protecting aquaculture, making the use of chemicals obsolete” points out Prof. Schmeller. Such a replacement of chemicals must become an essential part of the transformative change, as recently called for by the Intergovernmental Science-Policy Platform for Biodiversity and Ecosystem Services (IPBES). Human society needs to undergo such a change to preserve the live-support system nature provides to humans and all life on earth.


Global Assessment:



Thijs Frenken, Ramsy Agha, Dirk S. Schmeller, Pieter van West, Justyna Wolinska (2019). Biological Concepts for the Control of Aquatic Zoosporic Diseases. Trends in Parasitology, doi:10.1016/

Schmeller, D. S., Blooi, M., Martel, A., Garner, T. W. J., Fisher, M. C., Azemar, F., Clare, F. C., Leclerc, C., Jäger, L., Guevara-Nieto, M., Loyau, A., & Pasmans, F. (2014). Microscopic aquatic predators strongly affect infection dynamics of a globally emerged pathogen. Current Biology, 24 (2): 176-180.

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