Researchers from AZTI and Biopolis S.L. in Spain and the University of Aveiro and Aguacircia Aquaculture in Portugal have participated in the Enviphage project, which evaluated the effect of using bacteriophages to fight pathogens responsible for fish diseases as well as the environmental and intestinal bacteria communities of the fish.

Aquaculture is the world's fastest-growing food production sector and is a complementary activity to fishing, which provides more than 50% of the world's supply of fish and seafood.

However, the aquaculture sector also faces problems related to the development and rapid transfer of bacterial infections on fish farms. The most common treatment to prevent such infections and reduce the corresponding heavy economic losses is the use of antibiotics.

However, despite the fact that health authorities have called for responsible use of antibiotics, their prolonged use in aquaculture has led to the development of resistant bacteria, AZTI said. On the other hand, many of these antibiotics are non-specific, acting not only against the problematic pathogen but also against other bacteria naturally present in the environment.

All of this, together with consumers' call for antibiotic-free products, has led to the search for alternative solutions to the use of antibiotics to fight bacterial infections, particularly in the early stages, when vaccination is not possible and the maintenance of the bacterial ecosystem is vital.

Therapy with phages instead of antibiotics is a highly promising option in aquaculture to control the transfer of bacteria that cause important losses or that may be harmful to consumers. The use of phages, which infect and destroy bacteria, would significantly reduce the environmental impact of fish farms while increasing their profitability by lowering mortality in the early stages of the breeding process, AZTI said.

Different research projects have shown very promising results at the laboratory level, but before being able to use phages at a commercial level, it was necessary to know about the impact of their use on the environment and marine ecology.

The Enviphage project sought to address this gap between the laboratory and industrial-scale treatment. In the search for a strategy that enables the health of farmed fish to be improved without affecting the environment or consumer safety, this project has worked to identify phages that infect and eliminate the pathogens of interest without affecting the environmental and intestinal bacteria communities -- two critical points for the use of this technology in fish farms, according to the announcement.

Throughout the Enviphage project, the most promising bacteriophages with specific action against the pathogens of relevant fish were selected for their use on a real scale. Later, following their production on an industrial scale, the phages were applied in fish farms. Their effectiveness has been proved in real conditions, and the impact of phage treatment on fish has been evaluated through veterinary monitoring and on the marine and intestinal bacterial communities through mass sequencing technologies and bacterial ecology studies.

The results obtained during 2017 show that the intestinal bacterial community of fish is not significantly affected following treatment with the selected phages, AZTI noted. It has also been shown that this treatment does not modify the marine bacterial population in the fish farm tanks or in the river where the fish farm is located, so it has zero impact or very limited impact on the bacterial ecology.

AZTI is a research technology center in Spain specializing in food and marine science.