Institute of Marine Research
Example of temperature variations in a aquaculture sea cage

Despite that a sea cage can contain fish for more than a million Euros the monitoring of cage environment and fish behaviour is typically kept at a minimum. The reasons for the low monitoring level are both lack of suitable monitoring equipment and lack of computer systems for handling and interpreting the large amounts of data. Having identified this deficiency we wanted to create a system for monitoring of cage environment, fish behaviour and automatic assessment of fish welfare in aquaculture sea cages. The prototype version of the Welfaremeter has been tested for two years in a commercial salmon farm showing promising results and we are now moving from prototype to a finished product. This second generation of the Welfaremeter is scheduled to be tested at two commercial farms from June 2010.


The Welfaremeter is a collection of products that together document and analyse the conditions in a sea cage. These products include different measuring systems as profiling CTD’s and echosounders, a database for safe storage of the data, an expert software program for analysis of the data and an internet application for easy viewing of the data and the results from the expert software.

Profiling CTD

Several studies show that the conditions in a sea cage can vary with season, during the day and throughout the water column (e.g. Johansson et al., 2007; Oppedal et al., 2010). The same studies also show that measuring water quality outside a sea cage gives limited information of the environment the fish are experiencing; e.g. Vigen (2008) observed highly variable and minimum 30% oxygen saturation inside a sea cage, even though the oxygen saturation outside the sea cage was near 100%. In consequence it is necessary to measure the environmental conditions frequently inside a sea cage, and for the entire water column. A central component of the Welfaremeter is therefore a buoy (APB505, SAIV AS, Norway) with a profiling CTD. The buoy winches the CTD up and down in the sea cage at predefined intervals measuring temperature, salinity, oxygen, fluorescence and turbidity for the entire water column of the sea cage.


In cages with a clear stratification in water quality farmed salmon position themselves in order to be close to their optimum environment (Johansson et al., 2006; Oppedal et al., 2010). Atlantic salmon (Salmo salar L.) have for instance been observed to prefer temperatures between 16 to18°C within a range of 11 to 20°C (Johansson et al., 2006). By including echosounder data we will know which water quality is actually experienced by the fish, thus providing more accurate input to the expert software’s models for fish growth and fish welfare (see below). Also if the fish position themselves at suboptimal water qualities this may be an indicator of disease or an immune compromised state. The expert system compares the experienced with the expected swimming depth as a behavioural indicator of the well-being of the fish. As an example: lack of activity towards surface feeding events may indicate poor welfare (Juell et al., 1994).

Database, expert software and internet application

The data from the different measuring systems are automatically stored in a central database. As soon as new data arrives in the database they are analysed by the expert software. In addition to looking for abnormal vertical position (see above) the software uses data about the water quality to calculate a welfare index from 0 (terrible welfare) to 100 (excellent welfare). This index is based on modelling of metabolic scope (the fish’s capacity to extract oxygen beyond their basic needs from the water) and is a measure of how much stress the fish can tolerate. The fish farmer can therefore use this index when managing meal times, feed amounts and to decide if operations (for instance cleaning of the nets) can be performed or should be postponed. Both the incoming data and the results from the expert system are shown in the internet application.

First trial of the second generation Welfaremeter

During the autumn of 2010 we will test the Welfaremeter system at two different commercial sites along the coast of Norway. The goal is both to test the robustness of the different parts of the Welfaremeter system and to evaluate and improve the expert software. The expert software should be able to give the fish farmer daily information to improve fish welfare and hence the productivity of the fish farm. We will also add additional data sources as manual input via the internet application, data from a probe that measures water quality outside the cage and SmartTag. SmartTag is a system developed by Nofima Marin and Thelma AS (Norway) that registers breathing patterns of individual fish.


The development of the Welfaremeter started as part of the EU project 022720 FASTFISH and the RCN project 179878 Velferdsmåler and is now continued in the RCN project 190259 WELFARE-TOOLS. W-T is also funded by FHF and Nord-Trøndelag Fylkeskommune. We would also like to thank Marin consultant Per Andersen, BTO, SAIV AS, Morten Hammersland programvare, Tendo Tech AS, STM-maskinering AS and ARGUS Remote Systems AS who has invested a lot of time and enthusiasm in the project.


Johansson D., K. Ruohonen, A. Kiessling, F. Oppedal, J-E Stiansen, Kelly M., J-E. Juell. 2006. Effect of environmental factors on swimming depth preferences of Atlantic salmon (Salmo salar L.) and temporal and spatial variations in oxygen levels in sea cages at a fjord site. Aquaculture 254: 594-605.

Johansson D., J-E. Juell, F. Oppedal, J-E. Stiansen, K. Ruohonen. 2007. The influence of the pycnocline and cage resistance on current flow, oxygen flux and swimming behaviour of Atlantic salmon (Salmo salar L.) in production cages. Aquaculture 265: 271-287.

Juell J-E., A. Fernö, D. Furevik, I. Huse. 1994. Influence of hunger level and food availability on the the spatial distribution of Atlantic salmon, Salmo salar L., in sea cages. Aquac. Fish. Manage. 25: 439-451.

Oppedal F., T. Dempster, L. H. Stien. 2010. Environmental drivers of Atlantic salmon behaviour in sea-cages: a review. Submitted to Aquaculture.

Vigen J. 2008. Oxygen variation within a seacage, Master Thesis. Department of Biology. University of Bergen, Bergen, 73 pp.


Tore S. Kristiansen
Research group leader
+47 92069918

Lars H. Stien
+47 47291029

Research group

Animal welfare

Institute of Marine Research University of Oslo Nofima ARGUS | Remote Systems AS SAIV AS Plastinvent AS