Stine Wiborg Dahle:
Recirculating aquaculture systems (RAS) are widely used in the production of salmon smolt today, both in Norway and around the world, while lumpfish are produced in traditional through-flow systems (FTS). RAS consists of many different bacteria, which directly affect most water chemical variables and fish health, both positively and negatively. In order to facilitate the good bacteria, one must therefore think carefully through operation and design, which affects the bacterial communities. However, this is an operational challenge and more knowledge is needed about microbial community composition in such systems. The PhD candidate's work has shed light on microbial compositions in commercial RAS for the production of salmon smolts and roe biscuits. This has been done by:
1) An experiment with lumpfish in RAS with various water treatments and flow-through systems as a reference, at a commercial producer, Ecomarine Seafarm, in collaboration with Let Sea AS, for a total of 160 days.
2) Two studies where the candidate has performed sampling of water and biofilm at two commercial RAS facilities for salmon smolt over 15-20 months.
The experiment with lumpfish showed that it is possible to control which microbial compositions are formed in both water and biofilm in RAS by different water treatments. The experiment also showed that RAS gave a higher survival, better gill health and better composition of bacteria than flow-through, which can be recommended in the production of lumpfish. On the other hand, disinfection before fish tank should be avoided in RAS due to poorer microbial water quality and poorer gill health of the fish.
The studies from the Atlantic salmon RAS facilities have provided new knowledge about how the microbial compositions vary over time in commercial facilities. The microbial communities are very complex and vary both within production batches but also between production batches, according to physical and chemical water quality as well as different procedures used.
The PhD candidate's activities have so far resulted in 3 scientific publications and a number of popular science articles
The candidate's research has been aimed at developing new technology for measuring physiological data in free-swimming farmed fish. In the first part of the PhD period, focus was on identifying new sensor types, and the development of an intelligent sensor platform for these that can be implanted in fish. This work resulted in an implant that measures acceleration, rotation rates, compass direction, magnetic field, temperature, electrocardiogram (ECG) and photoplethysmogram (PPG). This enables the calculation of an activity indicator, a robust method for estimating heart rate based on two independent measurement principles and a potential for estimating oxygen saturation in arterial blood, something that has never been done for fish before. Initial proof-of-concept experiments for the implant and the sensors were performed as terminal in-vivo experiments on fish under general anesthesia, and resulted in data that were promising in terms of measuring both heart rate and oxygen saturation.
For such implants, the fish's movements can interfere with the measurements so that it becomes difficult to extract the desired signal (here heart rate and oxygen saturation) from sensor data. The second half of the PhD project was therefore focused on investigating whether the implant provides good data for awake fish in motion. This was first investigated by placing implanted fish in a swimming tunnel and water oxygenation artificially reduced to create hypoxic conditions that can be reflected in the oxygen saturation of the blood. Data analysis is complete, and results indicate that both heart rate and oxygen saturation are possible to measure on live and free-swimming fish if one compensates for the movements before calculating these parameters. The results are currently being published.
A mathematical model to estimate the response of the PPG sensor to salmon blood with different oxygen saturations has also been developed. This model aims to map data from the PPG sensor to absolute values for oxygen saturation, and is calibrated and validated using blood samples with different saturations.
A final experiment using implanted fish released into a tank has been carried out. Recorded acceleration and rotation data will be used to examine and compare various activity indicators including tail beat rate, that can potentially be used to compensate for data from PPG and ECG with respect to movement.
The PhD candidate's activities have so far resulted in 4 scientific publications and a new implant with biosensors primarily for use in Atlantic salmon. A further 2 publications and 2 manuscripts are planned before the end of the project period.