Understanding the tolerance limits of fish is crucial for developing aquaculture operations that ensure good animal welfare. However, there exist little data describing the physiological responses in farmed Atlantic salmon, much because the technological tools for taking such measurements have not existed. Recent advances in electronic implants have enabled concurrent measurement of electrocardiogram (ECG) and photoplethysmograms (PPG) in salmon that can be used for robust estimation of HR and oxygen saturation in arterial blood (i.e., SpO2/pulse oximetry) if appropriate strategies for motion artifact and light scattering compensation can be realized. To enable pulse oximetry for farmed Atlantic salmon (and fish in general), two experiments have been conducted. In Experiment 1, PPGs were obtained from salmon induced to swim at two different water currents under normoxic conditions. By using two water currents, the resulting data provided a foundation for developing methods for motion artifact compensation. Data from this experiment were also used to calculate an average light scattering parameter using the modified Beer-Lambert law, under the assumption that SpO2 was 100% for individual fish. In Experiment 2, fish were placed in a swim tunnel and subjected to hypoxic conditions and corresponding changes in SpO2 were estimated using the motion artifact and light scattering compensation approaches from Experiment 1.Results show that the suggested compensation approaches gives SpO2 estimates within the expected range (95% to 100%) under normoxic conditions. Under hypoxic conditions, changes in SpO2 that coincide with experiment events were observed, demonstrating that PPGs can be used to quantify such changes. The results from this pilot study therefore extend the selection of physiological parameters feasible to measure using electronic implants for Atlantic salmon. In doing so, the scope for physiological measurements is extended such that an improved understanding of physiological responses and tolerances in Atlantic salmon farming can be acquired, and ultimately be used to improve animal welfare in fish production.

The tailbeat frequency (TBF) together with tailbeat amplitude (TBA) of fish are tightly correlated with swimming speed. In addition, these parameters can be used as indicators of metabolic rate and general activity level, provided that appropriate calibration studies have been performed in the laboratory. If an implantable bio-logger could measure TBF and TBA, it would, therefore, have great potential as a tool to monitor swimming behaviours and bioenergetics over extended periods of time in free roaming fish within natural or farm environments. The purpose of this study was, therefore, to establish a method for deriving accurate TBF and variations in TBA from activity tags that log high-resolution acceleration data. We used 6 tagged Atlantic salmon ( Salmo salar ) of ≈1 kg and subjected them to two types of swim trials in a large swim tunnel system. Test speeds were either incrementally increased in 20-min intervals until steady swimming ceased, or constant speed of 60 cm s −1 was given in a 4-h sustained test. The TBFs were visually observed by camera and compared with computed values from the activity tags. In the incremental trials the TBF increased linearly with swimming speed, while it remained constant during the 4 h of sustained swimming. The TBFs measured by activity tags were within ± 0.1 beat s −1 of the visual measurements across the swim speeds tested between 30 to 80 cm s −1 . Furthermore, TBF and its corresponding relative swim speed were consistent between trial type. The relative TBA increased with swimming speed as a power function, showing that the fish relies on changes in both amplitude and frequency of tail movements when swimming at higher speeds, while adjustments of amplitude only play a minor part at lower speeds. These results demonstrate that TBFs can be measured accurately via activity tags, and thus be used to infer swimming activities and bioenergetics of free roaming fish. Furthermore, it is also possible to estimate changes in TBA via activity tags which allows for more nuanced assessments of swimming patterns in free roaming fish.

In this study, a general control framework for autonomous operations in highly complex and dynamically changing environments such as fish farms is proposed and experimentally validated. Since fish farms feature an environment that includes fish, deformable flexible structures and highly variable environmental disturbances, the framework is designed to interact with these. The proposed control approach integrates estimates of the cage structure dynamics and fish behavior, adaptive path planning and path following control concepts in one unified and compact framework that could be used to implement and demonstrate different concept studies in dynamically changing environments. The performance of the control framework is investigated though field trials using a remotely operated vehicle (ROV) in a commercial fish farm. Experimental results show that the proposed framework can be applied to challenging operations in fish farms.

Farmed aquatic animals represent an increasingly important source of food for a growing human population. However, the aquaculture industry faces several challenges with regard to producing a profitable, ethical and environmentally sustainable product, which are exacerbated by the ongoing intensification of operations and increasingly extreme and unpredictable climate conditions. Fortunately, bio-sensors capable of measuring a range of environmental, behavioural and physiological variables (e.g. temperature, dissolved gases, depth, acceleration, ventilation, heart rate, blood flow, glucose and l-lactic acid) represent exciting and innovative tools for assessing the health and welfare of farmed animals in aquaculture. Here, we illustrate how these state-of-the-art technologies can provide unique insights into variables pertaining to the inner workings of the animal to elucidate animal-environment interactions throughout the production cycle, as well as to provide insights on how farmed animals perceive and respond to environmental and anthropogenic perturbations. Using examples based on current challenges (i.e. sub-optimal feeding strategies, sub-optimal animal welfare and environmental changes), we discuss how bio-sensors can contribute towards optimizing the growth, health and welfare of farmed animals under dynamically changing on-farm conditions. While bio-sensors currently represent tools that are primarily used for research, the continuing development and refinement of these technologies may eventually allow farmers to use real-time environmental and physiological data from their stock as 'early warning systems' and/or for refining day-to-day operations to ethically and sustainably optimize production. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

We investigated the relationship between telemetry measurements of heart rate and swimming activity and the physiological status in farmed Atlantic salmon (Salmo salar) to assess the potential to use telemetry measurements as proxies for stress. Sensor tags measuring heart rate and swimming activity were surgically implanted into the peritoneal cavity of Atlantic salmon individuals kept in tanks. Four tanks were stocked with three tagged fish and four untagged cohabitants, while two additional tanks containing 16 untagged fish were used as reference groups. Following surgery, tagged fish were kept undisturbed for 14 days as acclimation period. All fish were then subjected to physical stress by reducing the tank water level in 4 consecutive rounds, after which they were left undisturbed for another ten days before the experiment ended. Plasma cortisol, glucose, lactate and osmolality were measured to assess stress levels from fish in the reference groups before and after being subjected to stressing and from all fish at the end of the experiment. Both heart rate and swimming activity rose after the stress treatment, remaining elevated for 24.5 and 16.2 Hrs respectively. Glucose, plasma cortisol, lactate and osmolality levels were significantly greater when measured immediately after stress. Results from the experiment indicate that heart rate and swimming activity can be used as proxies for fish stress, thus opening the possibility for on-line stress monitoring in full scale production.

A major trend in marine aquaculture is to move production to more exposed sites with occasionally rough ocean current events. However, it is unclear whether fish will thrive in these extreme environments, since thorough descriptions of ambient current conditions with regards to fish welfare is lacking. In the present study, ocean current data were collected using acoustic Doppler current profilers at 5 exposed sites along the Norwegian coast over minimum periods of 5 mo. To evaluate welfare risks, current data was compared to known limits of swimming capabilities, such as onset of behavioural changes and critical swimming speeds (U-crit), of Atlantic salmon Salmo salar and lumpfish Cyclopterus lumpus. Specifically, at each site, current speeds were classified into 6 categories based on expected impact on swimming behaviours of Atlantic salmon, and duration of currents within each category were inspected using a homogeneous and non-homogeneous criterion for the water column. Current speeds were then compared with projected U-crit at relevant temperatures and fish sizes of Atlantic salmon and lumpfish. Furthermore, a detailed characterization of extreme events at the most exposed site was performed. Of the 5 locations, only 1 exceeded the U-crit of Atlantic salmon, while all sites featured currents above U-crit of lumpfish for up to 33 h at a time. These results suggest that responsible Atlantic salmon farming is possible at sites considered exposed, while lumpfish should be restricted to more sheltered environments. The presented method can be applied for other aquaculture fish species if adequate data are available.

This paper presents a method for Real-Time Hybrid Model testing (ReaTHM testing) of ocean structures. ReaTHM testing is an extension to traditional hydrodynamic model-scale testing, where the system under study is partitioned into physical and numerical substructures. The physical and numerical subsystems are connected in real-time through a control system. Based on experience with various ReaTHM tests, a general method for ReaTHM testing of ocean structures has been proposed. An experimental case study was carried out to illustrate the proposed method. The study was conducted in a state-of-the-art hydrodynamic laboratory, where a physical cylindrical buoy was placed in a still-water basin. Horizontal mooring loads from a numerical mooring system, which were modelled using the nonlinear finite element software RIFLEX were actuated onto the physical substructure. System performance was verified through comparison with a physical horizontal mooring system consisting of physical springs.

The aim of this study was to demonstrate the feasibility of acoustic telemetry for monitoring fish during farm operations and gather knowledge about Atlantic salmon responses during crowding and delousing events in a commercial sea-cage. 21 fish were equipped with a novel transmitter tag type using data from pressure sensors and accelerometers to compute swimming depth and swimming activity of individual fish. The fish were monitored over four months, during which they were subjected to three thermal delousing events. In the periods before and after delousing, the fish generally exhibited a circadian rhythm in both swimming activity and depth, with high activity and deep swimming during daytime and low activity and shallow swimming during night. Swimming activity recorded during crowding and delousing events was significantly higher than background swimming activity levels registered a day before and after delousing. Although activity levels differed significantly between the three events and between the different stages within each event, the highest activity levels were consistently measured during thermal treatment. Swimming depth differed significantly between delousing events and was strongly influenced by daylight. In summary, crowding and delousing induced increased movement in the fish, while swimming depth appeared to be less sensitive to these operations. The conclusion of the study is that acoustic telemetry is a suitable tool for monitoring fish during challenging operations such as crowding and delousing, as well as during normal cage management. Moreover, this study provides new knowledge on how the behaviour of Atlantic salmon may be affected by delousing.

We tested if it is technically feasible to monitor fish in real-time in full-scale commercial fish farms using acoustic telemetry. 31 Atlantic salmon were equipped with acoustic transmitter tags containing depth sensors. Tagged fish were monitored for three months in two industrial scale sea-cages containing 180000 and 150000 fish, respectively. Each cage was fitted with two prototype acoustic receiver units designed to collect, interpret and store the information transmitted by the acoustic transmitter tags. Ten in each cage were also equipped with Data Storage Tags (DSTs) containing depth sensors to record individual-based datasets for comparison with the acoustically transmitted datasets. After compensation for sample loss caused by expected acoustic interference between the transmitter tags, the resulting dataset revealed that the receiver units collected 90-95% of the signals in both cages. Acoustic communication conditions in the sea-cages were not strongly impaired by factors such as fish density and local noise. Further, the dataset from the acoustic transmitters had comparable resolution and quality to that produced by the DSTs. However, acoustic tags provide data in real time and enable farmers to respond to the received information with farm management measures, whereas archival tags such as DSTs need to be retrieved and downloaded and hence have no real-time applications. We conclude that acoustic telemetry is feasible as a method to monitor the depth of fish in real-time commercial aquaculture.