Introduction
Monitoring and control systems are an integrative part of the recirculation aquaculture systems (RAS), installed to provide accurate, real-time information on system status and performance, and to prevent catastrophic loss due to equipment or management failures (Timmons and Ebeling, 2007). Water quality monitoring is a part of the daily RAS management. It is both time consuming and often requires skilled personal with knowledge in water chemistry. Number of on-line probes for continuous measurement of water quality are currently available on the market, however they are not custom made for use in aquaculture systems and do not provide the necessary accuracy of measurements for application in aquaculture.
Contrary to the water quality, the real time monitoring of fish status is usually not an integrated part of the automatized monitoring systems within RAS. The use of cameras in turbid RAS water is limited by the proximity of the fish, light availability and the data analysis is time consuming. Changes in swimming activity can reflect how a fish is sensing and responding to its surrounding environment (Martins et al., 2012) and a number of water quality parameters can affect swimming of farmed fish (Conte, 2004; Espmark and Baeverfjord, 2009). The acoustic acceleration transmitter tags (Motion tag) can be used to measure swimming activity of fish and the development of the receiver equipment technology has also allowed the continuous real time data access through internet or local network solutions.
The results from two studies will be presented. In the first study a multi-sensor platform for continuous monitoring of water quality in RAS with a customized miniaturized automated colorimetric analyzer (MACA) for the measurement of total ammonia nitrogen (TAN) and nitrite-nitrogen (NO2-N) in aquaculture was developed and has been tested. In the second study we have evaluated the use of implanted Motion tag for monitoring of Atlantic salmon swimming activity in RAS at different water qualities.
Methods
Testing of a multi-sensor platform for continuous monitoring of water quality in RAS
The performance of a multi-sensor platform for continuous monitoring of water quality was tested in the Nofima Centre for Recirculation in Aquaculture during production of Atlantic salmon (n=10520, start weight of 11 g ind-1) in freshwater RAS. The RAS was operating at the 99.4% of recirculation degree of the total flow that was on average 492 ± 9 L min -1 (± SD) and the average daily system volume exchange rate was 12.7%. A platform consisting of the Pacific control unit and five on-line probes (salinity, O2, pH, TGP, CO2) was installed in the degassing sump for continuous measurements of the water quality within RAS. Data logging, monitoring and trending was done via AQUAlity software and SQL server 2012. MACA was not integrated into the platform and TAN and NO2-N measurements were done in the lab using the water collected from the RAS. Regular water quality measurements were done using standard lab and commercially available instruments in order to establish accuracy, response time and maintenance requirements of the platform.
The use of Motion tag for monitoring of Atlantic salmon swimming activity in RAS
Twelve salmon postsmolts (804 ± 156 g) were individually tagged and distributed evenly in three tanks containing salmon postsmolts at start density of 50 kg m-3. The tanks were supplied with RAS water with an average temperature of 14.2 ± 0.7oC and reared under continuous light regime. The average recycled water flow rate in the system during the trial was 1105 ± 9 L min-1 (99.2 ± 0.2 recirculation rate), and a daily water system volume exchange rate of 21 ± 4 %. Following initial recovery after tagging and acclimatization (7 days), acceleration data were continuously logged for one month, including one week long treatment periods with exposure to hyperoxic (170% O2 saturation) and hypoxic (60% O2 saturation) conditions, and increased (140 L min-1) and decreased water flow rate (55 L min-1) within the tanks.
Results and discussion
The results of the multi-sensor platform testing indicate the importance of the proper maintenance of the on-line probes as the formation of the biofilm on the surface of the pH, CO2 and O2 probe affected significantly the accuracy of the continuous measurements. Cleaning of the pH probe caused an immediate increase in measured pH of between 0.1 and 0.3. This indicates that, in systems with high biological loading, a daily cleaning routine is necessary. Alternatively the use of probe cleaning systems commonly used in waste-water treatment plants could be used (Kolarevic et al., 2011). In addition, an offset of 5 mg L-1 CO2 was recorded after on-line probe was operated for ten days without maintenance. The MACA reproduced stable measurement in the range between 0.05 and 2.5 mg L-1 of NO2-N and between 0.1 and 5 mg L-1 TAN measurements.
The use of Motion tags did not cause any mortality and all individuals increased their body weight during this study. The O2 manipulations reduced the swimming activity of Atlantic salmon in this study. On the contrary, changes in the recirculating water flow rate at the tank level increased the swimming activity. Atlantic salmon responded with a maximum recorded swimming activity to stress induced by system problems and consequent changes in the RAS environment. The results of this study indicate that Atlantic salmon responds quickly with changed swimming activity to changes in the water quality and acute stress caused by normal management routines within RAS.
Acknowledgements
The research leading to these results has received funding from the FP7 managed by REA Research Executive Agency (http://ec.europa.eu/research/rea) (FP7/2007-2013) under grant agreement number [286995] in a research for the benefits of SME associations, project AQUAlity: "Multi-sensor automated water quality monitoring and control system for continuous use in recirculation aquaculture systems" and was financed by Nofima as a part of the internal project: "Fish welfare and environmental biology" and by the Research Council of Norway as a part of the project "Fish welfare and performance in Recirculating Aquaculture Systems" (project number 186913).
References
Conte, F.S., 2004. Stress and the welfare of cultured fish. Applied Animal Behaviour Science 86, 205-223.
Espmark, Å.M., Baeverfjord, G., 2009. Effects of hyperoxia on behavioural and physiological variables in farmed Atlantic salmon (Salmo salar) parr. Aquaculture International 17, 341-353.
Kolarevic, J., Ciric, M., Zühlke, A., Terjesen, B.F., 2011. On-Line pH Measurements in Recirculating Aquaculture systems (RAS), Aquaculture Europe 2011. European Aquaculture Society, Greece, Rhodos, pp. 570-571.
Martins, C.I.M., Galhardo, L., Noble, C., Damsgard, B., Spedicato, M.T., Zupa, W., Beauchaud, M., Kulczykowska, E., Massabuau, J.C., Carter, T., Planellas, S.R., Kristiansen, T., 2012. Behavioural indicators of welfare in farmed fish. Fish Physiology and Biochemistry 38, 17-41.
Timmons, M., Ebeling, J., 2007. Recirculating Aquaculture. Cayuga Aqua Ventures, Ithaca, NY.