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HAVBRUK2-Stort program for havbruksforskning

Water disinfection strategies to improve Atlantic salmon parr production in freshwater recirculating aquaculture systems

Alternative title: Strategier for desinfisering av ferskvann i resirkuleringssystemer i akvakultur, for å forbedre oppdrett av lakseparr.

Awarded: NOK 8.0 mill.

The 2020 - 2021 project activities were executed successfully with numerous experimental tests and laboratory analyses conducted at Nofima, DTU Aqua and NTNU. This period was marked by a high inclusion of students in the project, with 7 MSc students, 1 PhD student and 1 post-hoc conducting their full or partial thesis within RASHealth activities. A popular science article titled ?RAS Scientist of the Future?, illustrates this very important milestone. A state-of-art research facility consisting of 9 RAS units within a pathogen approved facility (Tromsø Aquaculture Research Station) was inaugurated in the autumn of 2020. Since then, 5 experimental tests were conducted. A popular science article titled, ?Certain that RAS Technology is the Future of the Aquaculture Industry?, highlights this new facility, the RASHealth project and the potential in Atlantic salmon industry. The generation of new knowledge is well on its way. Research activities have included: 1) Test and development of various assays to quantify biofilm activity. In spring/summer 2021, a new respirometric method was applied to measure autotrophic and heterotrophic activity in biofilm on carrier elements from RAS. In summer/autumn 2021, another assay based on enzymatic hydrogen peroxide decomposition was tested and developed. Several experiments have been made to optimize flow-through time and ensure sufficient reproducibility. The assay seems to be able to quantify the overall bacterial activity of the biofilm. The method is expected to be used for various applications and will be integrated in 2022 tests in Nofima, Tromsø. 2) Determining the peracetic acid (PAA) concentration and administration in which no negative consequences are observed in Atlantic salmon parr performance was started autumn 2020 and concluded in autumn 2021. With this objective three experimental trials were conducted. Trial 1. investigated short PAA exposure: 9 PAA concentrations 0 ? 6.4 mg/L. Results from fish survival, feed intake, swimming behaviour, external welfare indicators and histology of skin and gill show no visible effects at concentrations below 1.6 mg/L of a short (1h) PAA exposure. Trial 2 investigated a four-week PAA exposure: 3 PAA concentrations 0, 0.1 and 1.0 mg/L and Trial 3 investigated a four-week PAA administration method: no PAA (control), Pulse (1 mg/L PAA/72h) and Continuous (1 mg/L). Results from fish growth performance, external welfare indicators and health show no visible effects at concentrations 0.1 and 1 mg/L of a continuous PAA exposure. Similar results were obtained when the method of PAA administration was tested, no visible effect on fish both at continuous and pulse treatments. Results of the RAS water quality show an increase of water turbidity and suspended bacteria counts when PAA is continuously added to maintain a 1 mg/L concentration. The overall preliminary conclusion for these series of trials is that concentrations below 1.6 mg/L (short exposure) and 1.0 mg/L (long exposure) do not affect Atlantic salmon parr welfare, health and performance. A continuous PAA administration seems to result in a more turbid water and bacteria presence RAS. 3) Evaluation of the infection contribution of two pathogen sources in RAS and the subsequent fish infection dynamics. With this purpose two trials were conducted in 2021 to simulate a biosecurity breach in RAS. In the first sub-trial, we spiked the system with Yersinia ruckeri via the intake water either once or for 3 consecutive days. In sub-trial 2, we employed infected stocks as vectors. Mortality was recorded in both trials and disease was identified to develop faster than the traditional bath exposure challenge in flow-through systems for this pathogen. Moribund fish exhibited the typical macropathologies for yersiniosis including blackening of skin color, exophthalmia and enlarged spleen. The bacteria were likewise re-isolated from the moribund fish. Direct swab test to detect the presence of the pathogen in the system yielded unconvincing results, and this may likely be due to the detection limit of the qPCR assay. This will be clarified by microbiota sequencing that is currently on-going. All these research activities have generated new basic knowledge and new practical recommendations or methods, which we believe can have an impact on RAS disinfection strategies. Now it is time for the project to increase activity on communicating results. A series of scientific manuscripts are now being drafted, abstracts for 2022 conferences being aligned, and industry workshops are being discussed with interested parties. Also, the popular science communication will shift its focus from communicating the project activities and project players to communicate the main project results.

Traditional Atlantic salmon production is shifting thousands of tonnes of fish production to recirculating aquaculture systems (RAS). Outbreaks of pathogens had led to severe losses in Norwegian RAS production and a recent survey revealed an uncertainty about the current disinfection protocols in terms of safety and efficacy. Therefore, it is necessary to gather more knowledge on how and where to apply water disinfectants in Atlantic salmon parr production in RAS, without compromising fish health, welfare and growth, biofilter bacteria or water quality. RASHealth project consists of six (6) work packages, four (4) research trials and fourteen (14) research tasks that are conducted by three (3) partners (Nofima, NTNU and DTU) in Norway and Denmark. The RASHealth’s ambition is: i) to develop new water treatment practices for Atlantic salmon parr in freshwater RAS using ozone or peracetic acid (PAA), ii) to improve RAS biosecurity by adopting disinfection strategies considering the pathogen vectors and reservoirs, iii) to document PAA’s effect on Atlantic salmon parr health, welfare and growth and, to evaluate two administration methods, iv) to develop and test a new assay to quantify biofilm activity during routine activities and v) to monitor the production of disinfection by-products and, their accumulation in the water. The project results and outputs will be disseminated by: i) conferences and workshop presentations, ii) teaching and lecturing, iii) on-site RAS facility workshops, iv) association with ongoing industry-based projects, v) scientific manuscripts in journals and vi) social and specialized media articles and newsletters. It is anticipated that the RASHealth will allow a standardized implementation of water disinfection strategies in RAS with substantial impact on the future planning, design, management practice and performance of RAS.

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HAVBRUK2-Stort program for havbruksforskning