UV irradiation alone or in combination with peracetic acid efficacy to control a Yersinia ruckeri breach in Atlantic salmon RAS
1. Purpose
Atlantic salmon parr-smolt flow-through systems are being replaced by recirculating aquaculture systems (RAS) in part due to a more controlled and stable production environment. RAS re-uses up to 90% of water; this leads to an accumulation of microorganisms, biometabolites and other substances in the rearing water. A series of water treatment units are required to maintain an optimal water quality. However, this RAS technological specificity poses a new challenge on how to disinfect the water without producing an adverse impact on the salmon’s health and welfare, and biofilter performance. Pathogen outbreaks in Norwegian parr and smolt RAS have accounted for hundreds of thousands of dead fish. The enteric redmouth disease agent Yersinia ruckeri is among the major pathogens that pose a significant challenge to Atlantic salmon production. Whether current routine disinfection protocol in RAS, such as ozone, are effective to control pathogen breaches is not fully understood. Moreover, a promising water treatment strategy to achieve a better disinfection is the use peracetic acid (PAA) in water. This was shown in wastewater research, whether it is relevant for RAS will be tested in the proposed trial. A second objective of this experiment is to determine the effect of ozone and peracetic acid (PAA) disinfection on biofilter performance in RAS. In specific, we will estimate the nitrifying and heterotrophic bacterial activity in biofilm formed on RAS biofilter carriers exposed to ozone and PAA by respirometry.
2. Distress
Fish will be exposed to Y. ruckeri and it is expected them to develop pathological signs associated to enteric redmouth disease. The pathogen challenge can also result in some fish mortality. Fish will be exposed to two oxidants (i.e. ozone and PAA), which have the potential to trigger oxidative stress.
3. Expected benefit
The current application aims to provide relevant data on ozone and PAA potential to prevent or control a pathogen breach in Atlantic salmon RAS. These results will be crucial to design disinfection strategies and improving biosecurity in Atlantic salmon RAS production. Further develop a potential on-site tool of monitoring and diagnosis for RAS biofilter and a better understanding of biofilm on the carriers, which would benefit biofilter design and water quality management in RAS.
4. Number of animals and what kind
One thousand eight hundred (N= 1800, appr. 10 g) mix-sex Atlantic salmon (Salmo salar) parr are proposed to be used in this trial.
5. How to adhere to 3R
Replace: It is not possible as it is necessary to use live fish to assess the disinfection efficacy of ozone and PAA in preventing fish to develop enteric redmouth disease.
Reduction: The number of fish requested is a minimum replicated sample to give reliable scientific results. The experiment will be performed in small tank units, which reduces the number of fish need.
Refinement: The design of trial considers the knowledge from previous ozone tests (Disinfect, CtrlAQUA SFI, NRC; FOTS ID 28220), PAA concentration assessment on Atlantic salmon (FOTS ID 24128) and Yersinia ruckeri biosecurity breach in RAS (FOTS ID 26793). Moreover, fish will be held by experienced and qualified staff on Atlantic salmon handling and sampling. Humane end points are defined and, the experimental systems are design for optimal rearing conditions for Atlantic salmon.
Atlantic salmon parr-smolt flow-through systems are being replaced by recirculating aquaculture systems (RAS) in part due to a more controlled and stable production environment. RAS re-uses up to 90% of water; this leads to an accumulation of microorganisms, biometabolites and other substances in the rearing water. A series of water treatment units are required to maintain an optimal water quality. However, this RAS technological specificity poses a new challenge on how to disinfect the water without producing an adverse impact on the salmon’s health and welfare, and biofilter performance. Pathogen outbreaks in Norwegian parr and smolt RAS have accounted for hundreds of thousands of dead fish. The enteric redmouth disease agent Yersinia ruckeri is among the major pathogens that pose a significant challenge to Atlantic salmon production. Whether current routine disinfection protocol in RAS, such as ozone, are effective to control pathogen breaches is not fully understood. Moreover, a promising water treatment strategy to achieve a better disinfection is the use peracetic acid (PAA) in water. This was shown in wastewater research, whether it is relevant for RAS will be tested in the proposed trial. A second objective of this experiment is to determine the effect of ozone and peracetic acid (PAA) disinfection on biofilter performance in RAS. In specific, we will estimate the nitrifying and heterotrophic bacterial activity in biofilm formed on RAS biofilter carriers exposed to ozone and PAA by respirometry.
2. Distress
Fish will be exposed to Y. ruckeri and it is expected them to develop pathological signs associated to enteric redmouth disease. The pathogen challenge can also result in some fish mortality. Fish will be exposed to two oxidants (i.e. ozone and PAA), which have the potential to trigger oxidative stress.
3. Expected benefit
The current application aims to provide relevant data on ozone and PAA potential to prevent or control a pathogen breach in Atlantic salmon RAS. These results will be crucial to design disinfection strategies and improving biosecurity in Atlantic salmon RAS production. Further develop a potential on-site tool of monitoring and diagnosis for RAS biofilter and a better understanding of biofilm on the carriers, which would benefit biofilter design and water quality management in RAS.
4. Number of animals and what kind
One thousand eight hundred (N= 1800, appr. 10 g) mix-sex Atlantic salmon (Salmo salar) parr are proposed to be used in this trial.
5. How to adhere to 3R
Replace: It is not possible as it is necessary to use live fish to assess the disinfection efficacy of ozone and PAA in preventing fish to develop enteric redmouth disease.
Reduction: The number of fish requested is a minimum replicated sample to give reliable scientific results. The experiment will be performed in small tank units, which reduces the number of fish need.
Refinement: The design of trial considers the knowledge from previous ozone tests (Disinfect, CtrlAQUA SFI, NRC; FOTS ID 28220), PAA concentration assessment on Atlantic salmon (FOTS ID 24128) and Yersinia ruckeri biosecurity breach in RAS (FOTS ID 26793). Moreover, fish will be held by experienced and qualified staff on Atlantic salmon handling and sampling. Humane end points are defined and, the experimental systems are design for optimal rearing conditions for Atlantic salmon.
Etterevaluering
Forsøket er betydelig belastende.
Begrunnelse for etterevalueringen
The main aims of this study were achieved. The disinfection methods tested, i.e. ozone and PAA (peracetic acid), contributed to a reduction of fish infected with Yersinia ruckeri. While retrospective information from this experiment was sent to the Norwegian Food Safety Authority, there are still ongoing analyses on both fish tissues and data.
In total, 1800 Atlantic salmon parr were used in this experiment, the same as applied for. The severity was expected to be severe, but this was the case for just a few of the fish. For most of the fish the severity was mild to moderate. The bacterial challenge did not develop as initially expected i.e. few fish were infected and developed enteric redmouth disease with symptoms and low mortality (5 fish out 1800 fish).
The experiment model and number of animals used was necessary for the robustness of the results as there is no alternative technique available at present.
Fish were exposed to the minimum pain and stress necessary, and the rearing environment and careful handling were optimized for the fish. The specified humane endpoints worked well along with the scoring sheet. The method for euthanasia is reported to have worked well.
In total, 1800 Atlantic salmon parr were used in this experiment, the same as applied for. The severity was expected to be severe, but this was the case for just a few of the fish. For most of the fish the severity was mild to moderate. The bacterial challenge did not develop as initially expected i.e. few fish were infected and developed enteric redmouth disease with symptoms and low mortality (5 fish out 1800 fish).
The experiment model and number of animals used was necessary for the robustness of the results as there is no alternative technique available at present.
Fish were exposed to the minimum pain and stress necessary, and the rearing environment and careful handling were optimized for the fish. The specified humane endpoints worked well along with the scoring sheet. The method for euthanasia is reported to have worked well.