The development of novel decontamination technologies in aquaculture , is important due to rising microbial resistances against the commonly used processes based on UV and ozone [1]. C old atmospheric plasma (CAP) is a physical technology, leading to physico-chemical reactions responsible for the inactivation of microorganisms. Previous studies on the antimicrobial efficacy showed promising results against genera like Vibrio and Aeromonas which are known to be harmful to fish [2]. This suggests CAP may be suitable for decontamination in recirculating aquaculture systems (RAS). But besides a sufficient efficacy and the sustainability of a new technology, the fish welfare has to be ensured or even improved . Thus , the safety of CAP was examined by various assays determining the potential toxicity and mutagenicity.
Therefore, a possible risk of the plasma application was analysed by an acute fish cell toxicity test of the Organisation for Economic Co-operation and D evelopment (OECD) [3] and a bioluminescence assay based on Aliivibrio fischeri [4] . Mutagenic potential was determin ed by the test, using the microorganism Escherichia coli WP2 uvrA [5]. To assess the plasma application, the possibility of a bromate formation was also investigated. Bromate may be produced by plasma-mediated oxidation processes and can be toxic to aquatic organisms . For the plasma treatment, a model aquaculture water based on analytical results of RAS water from a baltic sturgeon stock was designed. A volume of 500 ml was treated with a pin-to-liquid discharge for 30 minutes. This plasma-treated solution was used for all test assays.
The results of the toxicity tests showed a consistent high vitality of the fish cells (RTgill-W1 cell line) up to 50% CAP treated solution. For the bioluminescence assay whereas, lower amounts of treated solution led to a toxicity, quantifiable by the luminescence intensity correlating to the bacterial vitality. The bacterial mutagenicity testing revealed no indication for a mutagenic potential. No generation of the toxic agent bromate by plasma was detected.
In conclusion, the performed tests showed a low toxicity potential of CAP treated model aquaculture water under the chosen test conditions . Based on the results, a concentration between 20% and 50% of CAP treated solution should be used for decontamination in RAS, while not harming the fish. To finally ensure a safe use of CAP for aquaculture additional tests are necessary. The results of the preliminary experiments show, that CAP is a promising technology that can be suggested for use in RAS after further investigations.
1. Liltved, H., et al., High resistance of fish pathogenic viruses to UV irradiation and ozonated seawater. Aquacultural Engineering, 2006. 34(2): p. 72-82.
2. Halpern, M. and I. Izhaki, Fish as Hosts of Vibrio cholerae. Frontiers in microbiology, 2017. 8: p. 282-282.
3. OECD, Test No. 249: Fish Cell Line Acute Toxicity - The RTgill-W1 cell line assay. 2021.
4. DIN EN ISO 11348-3:2009-05 Water quality - Determination of the inhibitory effect of water samples on the light emission of Vibrio fischeri (Luminescent bacteria test) - Part 3: Method using freeze-dried bacteria (ISO 11348-3:2007); German version EN ISO 11348-3:2008
5. Gatehouse, D., Bacterial Mutagenicity Assays: Test Methods , in Genetic Toxicology: Principles and Methods, J.M. Parry and E.M. Parry, Editors. 2012, Springer New York: New York, NY. p. 21-34.