Disease and treatment in freshwater recirculation aquaculture

Workshop Coordinators:   Perttu Koski: perttu.koski@evira.fi
Finnish Food Safety Authority Evira, Elektroniikkatie 3, FI-90590 Oulu, Finland

Workshop Short report

After the opening of the workshop by Perttu Koski, an introduction to the fish health challenges in recirculation aquaculture was presented by Development Director Tapio Kiuru from the aquaculture development firm Arvo-Tec Oy, Huutokoski, Finland. The different circumstances from those of flow-through aquaculture – like high fish and pathogen densities, limited medication possibilities, in many cases newer or less studied cultured species – make recirculation facilities prone to disease problems. Tapio addressed the most important water treatment methods, solid removal, biofilters and oxygen addition. Water quality management causes the highest costs for recirculation aquaculture and there are different issues in the planning, start-up and production phases of the recirculation aquaculture systems (RAS). In most cases the first aid in diseases in RAS consists of the reduced feeding of the fish, increased water flow or exchange, increased pumping and addition of more oxygen and rock salt into the water.
Torsten Snogdal Boutrup (DTU Veterinary, Section for Virology, Division for Fish Diseases, Copenhagen, Denmark) told about disease problems in Danish RAS, especially in the relatively new model farm system, which has been initiated in order to decrease the environmental effects of Danish rainbow trout farms. In many cases the rational way of taking live fish into the farms, the all in –all out principle, the possibility of treating fish in single tanks or by any means have been forgotten in starting and maintaining the RAS. This is not inherent to RAS, but a common mistake in the planning, building and management. The fish taken to a certain unit of a RAS should be of similar immunological status and possible to take out at the same time. This would require better planned fish buys and movements than the common ones today. In the Danish model farm system the use of antibiotics is lower, and the use of formalin higher than in traditional aquaculture. Bacterial gill disease and Ich are the biggest killers of fish.
Thomas Wahli (National Fish Disease Laboratory, Centre for Fish- and Wildlife Health, Institute of Animal Pathology, Vetsuisse Faculty, Bern, Switzerland) summarized disease problems found in Swiss recirculation aquaculture of perch, sturgeon and rainbow trout. Viral diseases (perch Rhabdovirus disease, probably Herpesvirus disease of sturgeon and sleeping disease of rainbow trout) have caused problems. Even 40-100% mortalities in young starlet, when they have been less than 6 months old, have been observed. Other disease problems faced include microphtalmia, cataract and other eye pathologies in perch. These are followed by Lactococcus garviae and motile Aeromonas infections. The problems at 2 farms of 4 have originated from importation of diseased fish in Switzerland. Again, the impossibility of emptying the farms or parts of them has greatly hindered treatments and eradication or made them totally impossible in economic terms.
Miroslava Paliková (University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic) told about bacteriological and parasitological conditions encountered at a farm having rainbow trout, charr (and their crossings) and sturgeon. The abstract P-283 can be found in the proceedings of the EAFP 2013 conference.
Anna Maria Eriksson-Kallio (Finnish Food Safety Institute Evira, Helsinki, Finland) gave information of a research project addressing on-line water parameter monitoring and fish health in production scale RAS. In the project water quality factors like ammonia, NO2, NO3, O2, pH, alkalinity are associated with frequent health monitoring of rainbow trout.
The 40-50 participants of the workshop appeared to share the view of Brit Hjeltnes, who suggested a wider forum to exchange the experiences in different countries of disease problems, which seem to be common and needing concern by fish disease professionals.
The last part of the workshop was meant to handle disinfection and treatment of diseases in RAS. Klaus Knopf (Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany) presented a review of the use of ozone, ultraviolet light and low frequency ultrasound in the water disinfection of RAS. The abstract P-282 can be found in the proceedings of the EAFP 2013 conference.
Perttu Koski from Finnish Food Safety Authority Evira showed results of the concentrations of florfenicol in fish and water during and after treatment of whitefish (Coregonus lavaretus) in RAS. It was found that residues were under detection level by the end of the 500 degree day withdrawal time. On the other hand, low levels of florfenicol and the metabolite florfenicolamine were found in the water of the recirculation unit and fish not medicated via feed. The long and wide standing concentrations, which are under minimum inhibitory concentrations (MIC) of bacteria in the farming water, might possess a danger of development of resistant bacteria in the long run. This was, however, not found in the experiment.
The audience participated lively in the discussion. It was recognized that in the planning and building of RAS, fish health aspects should reserve a much more important role than today. This is especially important now because there are several enormous recirculation aquaculture projects going on European fish farming. Otherwise, the economic and environmental benefits of the RAS will be greatly threatened in addition to the serious problems caused to fish health and welfare.

Plan for the future

It was commonly agreed that there is a need for a wider workshop on the matters shortly dealt in this meeting. That kind of larger workshop would hopefully bring fish disease scientists and other professionals interested in diseases of the recirculation aquaculture to present their recent results and share views of the prevention and treatment of diseases in RAS. RAS is still rather uncommon environment for most fish disease professionals and it is important to be able to keep contact in the future. A 2-3 day workshop will be organized in Helsinki, Finland during the autumn 2014. The Nordic Council of Ministers will support the workshop intended mainly for participants from the Nordic Countries, but some places might be possible for others, too.

EAFP members and other interested in such kind of workshop can contact the coordinator Perttu Koski.