The biological mechanisms behind H2S-Atlantic salmon interaction
1 Purpose
Hydrogen sulphide (H2S) has become increasingly prevalent in Norwegian salmon recirculating aquaculture system (RAS) facilities, with several events of mass mortality that have been mainly attributed to H2S. However, our understanding on how Atlantic salmon respond to H2S and the associated physiological consequences remain barely explored and documented. The series of studies described in this application aims to advance our understanding of the risks and impacts of H2S to the physiology of Atlantic salmon in recirculating aquaculture systems.
2 Distress
Salmon smolts will be exposed to sub-lethal concentrations of H2S. The ability of salmon to perceive these chemical signals will be blocked transiently by different drugs. The secondary effects of this exposure will be investigated by subjecting the fish to a simulated heatwave, handling-confinement stress, and oxidant treatment, which will affect the physiology to varying degrees.
3 Expected benefit
The proposed trial will provide experimental evidence of the risk of H2S in salmon health and welfare in RAS, which is one of the main issues in the last years in Norwegian aquaculture. This will be crucial in developing risk assessment protocols, mitigation strategies and early warning systems in farms. In a more broader perspective, the expected results will be beneficial in fostering a research-driven adoption of RAS-based farming in Norway.
4 Number of animals, and what kind
One thousand two hundred sevety five fish (1275, appr. 70 g at the beginning) mixed-sex Atlantic salmon (Salmo salar) post-smolt are intended to be used in the trials described in this application.
5 How to adhere to 3R
There is no other way to test the hypothesis in the study than performing a trial using live fish, nevertheless, we incorporated several strategies to reduce fish number and reduce distress to the fish. First, we will be using sub-lethal level of H2S that have been identified and tested earlier. Second, we incorporated several hypotheses in a number of sub-trials to maximise the use of fish in experiments and provide a through documentation the consequences of H2S exposure in salmon physiology. Third, humane endpoints are clearly defined and, the experimental systems are designed for optimal rearing conditions for post-smolts.
Hydrogen sulphide (H2S) has become increasingly prevalent in Norwegian salmon recirculating aquaculture system (RAS) facilities, with several events of mass mortality that have been mainly attributed to H2S. However, our understanding on how Atlantic salmon respond to H2S and the associated physiological consequences remain barely explored and documented. The series of studies described in this application aims to advance our understanding of the risks and impacts of H2S to the physiology of Atlantic salmon in recirculating aquaculture systems.
2 Distress
Salmon smolts will be exposed to sub-lethal concentrations of H2S. The ability of salmon to perceive these chemical signals will be blocked transiently by different drugs. The secondary effects of this exposure will be investigated by subjecting the fish to a simulated heatwave, handling-confinement stress, and oxidant treatment, which will affect the physiology to varying degrees.
3 Expected benefit
The proposed trial will provide experimental evidence of the risk of H2S in salmon health and welfare in RAS, which is one of the main issues in the last years in Norwegian aquaculture. This will be crucial in developing risk assessment protocols, mitigation strategies and early warning systems in farms. In a more broader perspective, the expected results will be beneficial in fostering a research-driven adoption of RAS-based farming in Norway.
4 Number of animals, and what kind
One thousand two hundred sevety five fish (1275, appr. 70 g at the beginning) mixed-sex Atlantic salmon (Salmo salar) post-smolt are intended to be used in the trials described in this application.
5 How to adhere to 3R
There is no other way to test the hypothesis in the study than performing a trial using live fish, nevertheless, we incorporated several strategies to reduce fish number and reduce distress to the fish. First, we will be using sub-lethal level of H2S that have been identified and tested earlier. Second, we incorporated several hypotheses in a number of sub-trials to maximise the use of fish in experiments and provide a through documentation the consequences of H2S exposure in salmon physiology. Third, humane endpoints are clearly defined and, the experimental systems are designed for optimal rearing conditions for post-smolts.
Etterevaluering
The Norwegian Food Safety Authority must retrospectively assess all severe experiments.
Begrunnelse for etterevalueringen
The trial provided the first evidence under controlled experimental conditions the risk and physiological consequences of chronic exposure to the assumed sub-lethal concentration of hydrogen sulphide (H2S). An important result was that previously though sub-lethal level of H2S, also considered as the recommended threshold, has high risk for progressive mortality.
The results showed that mucosal organs of salmon responded differently to H2S, the olfactory organ being the most sensitive. Chronic exposure to high level of H2S affected the responses of salmon to a secondary stressor. Interesting, it was documented that salmon could recover two weeks after terminating the chronic H2S exposure. The functional inhibition of olfaction stated in the application, was not performed due to limited fish number.
In this trial only 450 of 1275 approved fish were used. This was due to unavailability of healthy fish stock at the research station. The harm was classified as follows: 150 fish suffered mild, 150 fish suffered moderate-severe while 150 fish suffered severe distress. Mortality was recorded in fish that showed moderate-severe signs during the trial. The trial was supposed to run for six weeks, but it was terminated at week four due to progressive mortality. The researchers also stopped the H2S dosing 2-3 times during the experimental period due to erratic behavioural changes in the fish.
The researchers reported that they have developed some in vitro models that could be used to understand some biological processes underlying the H2S-mucosa interaction in fish. These models were published in a provisionally accepted paper in Frontiers in Physiology.
The design of the trial was appropriate. Though, several test concentrations and durations of exposure could have provided more in depth understanding of the H2S risk in salmon.
The use of experimental animals in the trial were reduced. RAS performed well with reduced number of fish, lower than the previously thought number for the system to operate at optimal conditions. The data from this trial will be shared with colleagues who are optimising the conditions of the newly installed experimental RAS, where this trial was conducted. Hopefully, it will be pivotal in identifying the minimum number of fish for each particular set-up.
Improvements in trials like this are the use of more H2S sensors and camera-based behavioural monitoring of the fish.
The results showed that mucosal organs of salmon responded differently to H2S, the olfactory organ being the most sensitive. Chronic exposure to high level of H2S affected the responses of salmon to a secondary stressor. Interesting, it was documented that salmon could recover two weeks after terminating the chronic H2S exposure. The functional inhibition of olfaction stated in the application, was not performed due to limited fish number.
In this trial only 450 of 1275 approved fish were used. This was due to unavailability of healthy fish stock at the research station. The harm was classified as follows: 150 fish suffered mild, 150 fish suffered moderate-severe while 150 fish suffered severe distress. Mortality was recorded in fish that showed moderate-severe signs during the trial. The trial was supposed to run for six weeks, but it was terminated at week four due to progressive mortality. The researchers also stopped the H2S dosing 2-3 times during the experimental period due to erratic behavioural changes in the fish.
The researchers reported that they have developed some in vitro models that could be used to understand some biological processes underlying the H2S-mucosa interaction in fish. These models were published in a provisionally accepted paper in Frontiers in Physiology.
The design of the trial was appropriate. Though, several test concentrations and durations of exposure could have provided more in depth understanding of the H2S risk in salmon.
The use of experimental animals in the trial were reduced. RAS performed well with reduced number of fish, lower than the previously thought number for the system to operate at optimal conditions. The data from this trial will be shared with colleagues who are optimising the conditions of the newly installed experimental RAS, where this trial was conducted. Hopefully, it will be pivotal in identifying the minimum number of fish for each particular set-up.
Improvements in trials like this are the use of more H2S sensors and camera-based behavioural monitoring of the fish.