Abstract
In this study, 12 farmed Atlantic salmon (~1200 g) were tagged with commercially available heart rate (HR) bio-loggers and maintained in a controlled fish tank laboratory environment at 9 °C on a 12 h day/night cycle for 13 weeks. Apart from one fish that had obtained severe wounds on the tail region in the beginning, the remaining fish survived the entire test period and displayed consistent and similar HR in response to the day/night cycles with peak HR midday during feeding. At the end of the experiment, untagged conspecifics had significantly higher weights, fork lengths and conditions factors, showing the bio-logger may have a long term negative impact on growth. However, tagged fish still gained weight during the trial. Resting HR, as measured at night and early morning, decreased significantly over the first 2–3 weeks, and remained stable at ~25 beats min−1 between week 3 and 10, highlighting that substantial time is required for complete recovery following implantation of the bio-logger. At the start of week 11, 12 and 13, crowding stress trials of 30 min were performed which elevated HR to 55.7 beats min−1, whereafter it took 24 h to recover normal HR. Emerging bio-logger technologies can provide otherwise unobtainable information on the physiology and behaviour in free swimming individual fish over long periods and has great potential as welfare assessment tools in aquaculture. However, the impact of the tag must be considered with regards to the general representativeness of untagged counterparts when interpreting data.
Highlights
Fish welfare in Atlantic salmon (Salmo salar) aquaculture is gaining increased attention from both consumers and producers (Branson, 2008; Noble et al, 2018)
In the present study, we found that resting heart rate (HR) of Atlantic salmon, as measured at night and early morning, continued to decrease until the third week of the experiment whereafter it remained stable for the remaining weeks
While it is a concern that implantation of the bio-logger impair growth for quite some time, the benefits of obtaining high quality physiological measurements of free swimming individuals over long periods of time in their ambient environment makes up for this concern, in our opinion
Summary
Fish welfare in Atlantic salmon (Salmo salar) aquaculture is gaining increased attention from both consumers and producers (Branson, 2008; Noble et al, 2018). Good welfare in aquaculture means that the fish remains healthy, show normal behaviours and have high growth rates (Huntingford and Kadri, 2014) This is obviously advantageous for the producer and allows the consumer to enjoy a product made in an ethical and responsible way. For thorough individual assessments of farmed Atlantic salmon, the salmon welfare index model has been developed where a range of physical traits are scored on netted fish (Stien et al, 2013; Folkedal et al, 2016; Noble et al, 2018) These methods either assess welfare indirectly through environmental monitoring, at the group level in rather crude manners, or only provide a single time point measurements of random individuals
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