Dissolved oxygen variability in a commercial sea-cage exposes farmed Atlantic salmon to growth limiting conditions

Understanding dissolved O2 flux in marine cages, and how individual fish respond to and experience such variation, is critical to optimizing growth and production performance of farmed salmon. We used a high resolution environmental monitoring system to create a 3-dimensional map of a commercial marine cage with respect to salinity, temperature and dissolved O2 through time, while also tracking the oxygen experience of 4 individually tagged Atlantic salmon. Despite all of the dissolved O2 measurements at the reference site being physiologically suitable for maximum growth, 1 in 4 of the recordings collected within the cage were below dissolved O2 levels known to reduce feed intake and growth. Recorded dissolved O2 in the cage ranged from 26 to 90% saturation with a high degree of vertical, horizontal and temporal variation. Poorest dissolved O2 conditions consistently occurred at night in the central and down-current cage positions. Dissolved O2 levels experienced by individual fish ranged from 30 to 90% saturation, with variation within 5 minute intervals as large as 32 percentage points. These results expand the current body of knowledge on environmental variability in marine cages, and provide valuable insights to aid farm managers in focusing mitigation and monitoring efforts when and where they are most needed.

[1]  H. W. Rasmussen,et al.  Three-dimensional deformation of a large circular flexible sea cage in high currents: Field experiment and modeling , 2015 .

[2]  A. Farrell,et al.  Oxygen uptake in Pacific salmon Oncorhynchus spp.: when ecology and physiology meet. , 2016, Journal of fish biology.

[3]  L. Stien,et al.  Atlantic salmon Salmo salar instantaneously follow vertical light movements in sea cages , 2015 .

[4]  G. Claireaux,et al.  Responses by fishes to environmental hypoxia: integration through Fry's concept of aerobic metabolic scope. , 2016, Journal of fish biology.

[5]  F. Page,et al.  Environmental conditions and occurrence of hypoxia within production cages of Atlantic salmon on the south coast of Newfoundland , 2012 .

[6]  W. W. Reynolds,et al.  Behavioural fever in teleost fishes , 1976, Nature.

[7]  A. Edwards,et al.  Marine Fish Cages—The Physical Environment , 1976 .

[8]  Frode Oppedal,et al.  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 , 2006 .

[9]  Jon-Erik Juell,et al.  An ultrasonic telemetric system for automatic positioning of individual fish used to track Atlantic salmon (Salmo salar L.) in a sea cage , 1993 .

[10]  J. L. Martin,et al.  Seasonal Changes of Dissolved Oxygen and Plant Nutrients in Seawater near Salmonid Net Pens in the Macrotidal Bay of Fundy , 1993 .

[11]  L. Stien,et al.  PIT tagged individual Atlantic salmon registrered at static depth positions in a sea cage: Vertical size stratification and implications for fish sampling , 2013 .

[12]  T. Dempster,et al.  Fluctuating sea-cage environments modify the effects of stocking densities on production and welfare parameters of Atlantic salmon (Salmo salar L.) , 2011 .

[13]  T. Kristiansen,et al.  Individual variation in swimming depth and growth in Atlantic salmon (Salmo salar L.) subjected to submergence in sea-cages , 2012 .

[14]  O. Folkedal,et al.  Submergence of Atlantic salmon (Salmo salar L.) in commercial scale sea-cages: A potential short-term solution to poor surface conditions , 2009 .

[15]  Jon-Erik Juell,et al.  The behaviour of Atlantic salmon in relation to efficient cage-rearing , 1995, Reviews in Fish Biology and Fisheries.

[16]  L. Stien,et al.  The Interaction between Water Currents and Salmon Swimming Behaviour in Sea Cages , 2014, PloS one.

[18]  L. Stien,et al.  Sea lice infestation level alters salmon swimming depth in sea-cages , 2016 .

[19]  R. Olsen,et al.  Effects of cyclic environmental hypoxia on physiology and feed intake of post-smolt Atlantic salmon: Initial responses and acclimation , 2012 .

[20]  J. Stiansen,et al.  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 , 2007 .

[21]  F. Oppedal,et al.  Swimming depth and thermal history of individual Atlantic salmon (Salmo salar L.) in production cages under different ambient temperature conditions , 2009 .

[22]  Pål Lader,et al.  Hydrodynamic interactions on net panel and aquaculture fish cages: A review , 2013 .

[24]  The effects of fish behaviour on dye dispersion and water exchange in small net cages , 1988 .

[25]  Michael Sievers,et al.  The oxygen threshold for maximal feed intake of Atlantic salmon post-smolts is highly temperature-dependent , 2016 .

[26]  K. Frank,et al.  Effects of a Shielding Skirt for Prevention of Sea Lice on the Flow Past Stocked Salmon Fish Cages , 2013 .

[27]  R. Olsen,et al.  Hypoxia tolerance thresholds for post-smolt Atlantic salmon: Dependency of temperature and hypoxia acclimation , 2013 .

[28]  A. Imsland,et al.  The effect of thermal acclimation on aerobic scope and critical swimming speed in Atlantic salmon, Salmo salar , 2017, Journal of Experimental Biology.

[30]  L. Stien,et al.  Environmental drivers of Atlantic salmon behaviour in sea-cages: A review , 2011 .

[31]  F. Oppedal,et al.  Thermo- and photoregulatory swimming behaviour of caged Atlantic salmon: Implications for photoperiod management and fish welfare , 2007 .

[32]  L. Stien,et al.  Skirt around a salmon sea cage to reduce infestation of salmon lice resulted in low oxygen levels , 2012 .

[33]  A. Imsland,et al.  Production performance of Atlantic salmon (Salmo salar L.) postsmolts in cyclic hypoxia, and following compensatory growth , 2014 .

[34]  T. Dempster,et al.  Oxygen gradients affect behaviour of caged Atlantic salmon Salmo salar , 2017 .

[35]  Yun-Peng Zhao,et al.  Experimental investigation of the reduction in flow velocity downstream from a fishing net , 2013 .

[36]  Dag Myrhaug,et al.  Average Flow Inside and Around Fish Cages With and Without Fouling in a Uniform Flow , 2012 .

[37]  H. Volkoff,et al.  The effect of intermittent hypoxia on growth, appetite and some aspects of the immune response of Atlantic salmon (Salmo salar). , 2013 .

[38]  T. Dempster,et al.  Group Behavioural Responses of Atlantic Salmon (Salmo salar L.) to Light, Infrasound and Sound Stimuli , 2013, PloS one.

[39]  O. Folkedal,et al.  Assessing swimming capacity and schooling behaviour in farmed Atlantic salmon Salmo salar with experimental push-cages , 2017 .