Need for oxygen injection in fish cage farms
The project started in 2001 by monitoring environmental conditions at the EWOS Innovation cage farms in Oltesvik and Grotnes in Rogaland. At these and other farms, both in Norway and Canada, dissolved oxygen concentrations inside and outside salmon cages was the focus of attention. RF-Rogaland Research has been involved in the program as research partner together with the company OxSeaVision (OSV) and EWOS Innovation.
Especially in summer and early autumn in 2002 the unusually high sea temperature (above 20ºC) caused stagnant growth and high mortality at many salmon farms in southern Norway. In addtion to the the high temperature, dissolved oxygen (DO) concentrations were low and fluctuating during the day. At several farms, DO concentrations as low as 3 – 4 mg/L were observed. Without doubt, the combination of high temperature and temporarily lethal DO deficit resulted in a total loss of several billions NOK for the Norwegian salmon industry during 2002 – 03!
The effects of reduced DO on adult salmon were also studied in tanks at EWOS Innovation Dirdal. Even at 8 – 10ºC, the trial clearly demonstrated lack of appetite, reduced growth and feed utilisation when DO concentrations were kept below 80% of saturation (corresponds to below 7 mg/L). EWOS Innovation is now constructing a new advanced research hall in Dirdal where the water temperature can be regulated to desired level. As a new joint project between EWOS Innovation and RF, the DO deficit tests with adult salmon will be repeated in 2004-05 at more typical summer temperatures, i.e. in the range 14 - 20ºC, in this new research facility.
In summer – autumn 2003, the sea temperature was more within a normal range and peaked at 18ºC towards the surface. Still we observed decreased DO levels as low as 50% of saturation within salmon cages in Oltesvik. Oxygen was added to several cages at DO drops below 80% of saturation and we observed increased growth and improved feed utilisation. This year, the cage monitoring will be continued at EWOS Innovation’s research facility in Lønningdal outside Bergen based on collaboration between EWOS and RF.
Oxygen injection in sea cages is even more a topical effort in several fish farming nations abroad. During summer, critical low DO concentrations in salmon cages in Tasmania have turned out to be a major limiting problem. After a recent demonstration, Tasmanian fish farming companies have ordered numerous OSV’s injection units in order to improve the cage conditions in summer.
Farming of yellowtail, a Tuna species, is a significant part of Japanese aquaculture. This highly demanded species attains prices of more than 60 NOK per kg and represents a total yearly income of about 10 billions NOK for the industry. Yellowtail is less vulnerable to DO drops than salmon but loses appetite at long-lasting concentrations below 4 mg oxygen/L. Most of the farms in southern Japan experience such conditions in July – October and the combination high Farming of yellowtail, a Tuna species, is a significant part of Japanese aquaculture. This highly demanded species attains prices of more than 60 NOK per kg and represents a total yearly income of about 10 billions NOK for the industry. Yellowtail is less vulnerable to DO drops than salmon but loses appetite at long-lasting concentrations below 4 mg oxygen/L. Most of the farms in southern Japan experience such conditions in July – October and the combination high temperature (above 27ºC) and low DO concentration actually stagnates the production for a couple of months every year.
During our recent visit to this region, both fish farmers and researchers expressed their interest of purchasing equipment for oxygen addition.
View of Kagoshima 3 December2003. Numerous Yellowtail farms occupy the bay (Photo: Keisuke Nakayama )
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