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

• Published in: Aquaculture 2018-02, Vol.486, p.122-129
• Main Authors: Solstorm, David, Oldham, Tina, Solstorm, Frida, Klebert, Pascal, Stien, Lars Helge, Vågseth, Tone, Oppedal, Frode
• Format: Article
• Language: English
• Subjects: Aquaculture; Behaviour; Dissolved oxygen; Fish welfare; Hypoxia; Salmo salar
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/j.aquaculture.2017.12.008

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 5minute 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. •Dissolved O2 recording tags were deployed on individual sea-caged salmon to explore the implications of dissolved O2 variability for salmon welfare and growth.•3-dimensional mapping of environmental conditions within the cage revealed a complex pattern of dissolved O2 variability across the cage width in addition to previously observed vertical and temporal heterogeneity.•The extreme variability of dissolved O2 conditions observed throughout the cage was mirrored in the experiences of individually tagged fish, with all tagged individuals being exposed to dissolved O2 conditions limiting to growth and production performance.