Effect of freshwater or hyposaline water exposure on adult lice and salmon physiology
1 Purpose
The salmon aquaculture industry continues to use freshwater (FW) to treat Atlantic salmon parasites, such as AGD or other gill diseases, and for the ectoparasitic salmon lice. Although industry standards have been in place for some time, and studies have investigated how long salmon lice can remain attached to the host during exposure to FW, little is known about the threshold of tolerance lice have towards freshwater with regards to their attachment strength after exposure. Similarly, there is little knowledge of the short-term physiological changes that occur in salmon during these FW treatments, particularly regarding the status of their red blood cells. This experiment aims to address both of these knowledge gaps, using FW and hypo-saline (low salinity) water treatments.
2 Distress
Sources of potential distress in this experiment would come from a) infection by salmon lice, and b) exposure to freshwater or hypo-saline water for up to 48 or 12 hours. Infection intensity is not intended to be higher than 4 adults per fish, which is known to be a low-moderate level for salmon of this size. Secondly, short-term exposure to freshwater is common practice in labs and commercial settings, and is not known to stress salmon.
3 Expected benefit
By pinpointing the exact exposure time that can weaken lice (instead of directly causing detachment), freshwater treatments could potentially be reduced in commercial procedures. Furthermore, expanding our knowledge of physiological changes of salmon during short-term FW or hyposaline water exposure will provide better-informed welfare practices.
4 Number of animals, and what kind
The experiment will use 525 Atlantic salmon post-smolts of approx. 200g, 365 of which will be infected with adult lice. These fish will be exposed to one of three treatments (seawater, freshwater, or hyposaline water baths) for up to 48 hours; 10 fish will be sampled at intervals, with groups separated by tanks so as to optimise blood sampling procedures. There will be 6-12 treatment duration groups, including a pre-treatment group that will provide the baseline. One group of fish will be exposed to FW without infection, so as to isolate the physiological effect of FW exposure without the influence of lice.
5 How to adhere to 3R
Replacement is not possible as a live host is required to the lice, as well as there is no substitute for models of salmon physiological responses. Reduction has been optimised with the number of treatment groups and replicate fish per group to ensure robust and valid results (particularly with blood measures which can be very variable). The experimental protocol, experience of technicians and researchers involved, and husbandry practice all contribute to refining this experiment to ensure minimal handling or procedural stress.
The salmon aquaculture industry continues to use freshwater (FW) to treat Atlantic salmon parasites, such as AGD or other gill diseases, and for the ectoparasitic salmon lice. Although industry standards have been in place for some time, and studies have investigated how long salmon lice can remain attached to the host during exposure to FW, little is known about the threshold of tolerance lice have towards freshwater with regards to their attachment strength after exposure. Similarly, there is little knowledge of the short-term physiological changes that occur in salmon during these FW treatments, particularly regarding the status of their red blood cells. This experiment aims to address both of these knowledge gaps, using FW and hypo-saline (low salinity) water treatments.
2 Distress
Sources of potential distress in this experiment would come from a) infection by salmon lice, and b) exposure to freshwater or hypo-saline water for up to 48 or 12 hours. Infection intensity is not intended to be higher than 4 adults per fish, which is known to be a low-moderate level for salmon of this size. Secondly, short-term exposure to freshwater is common practice in labs and commercial settings, and is not known to stress salmon.
3 Expected benefit
By pinpointing the exact exposure time that can weaken lice (instead of directly causing detachment), freshwater treatments could potentially be reduced in commercial procedures. Furthermore, expanding our knowledge of physiological changes of salmon during short-term FW or hyposaline water exposure will provide better-informed welfare practices.
4 Number of animals, and what kind
The experiment will use 525 Atlantic salmon post-smolts of approx. 200g, 365 of which will be infected with adult lice. These fish will be exposed to one of three treatments (seawater, freshwater, or hyposaline water baths) for up to 48 hours; 10 fish will be sampled at intervals, with groups separated by tanks so as to optimise blood sampling procedures. There will be 6-12 treatment duration groups, including a pre-treatment group that will provide the baseline. One group of fish will be exposed to FW without infection, so as to isolate the physiological effect of FW exposure without the influence of lice.
5 How to adhere to 3R
Replacement is not possible as a live host is required to the lice, as well as there is no substitute for models of salmon physiological responses. Reduction has been optimised with the number of treatment groups and replicate fish per group to ensure robust and valid results (particularly with blood measures which can be very variable). The experimental protocol, experience of technicians and researchers involved, and husbandry practice all contribute to refining this experiment to ensure minimal handling or procedural stress.