Oxygenation effects on temperature and dissolved oxygen at a commercial Atlantic salmon farm

As climate change continues to warm oceans and exacerbate deoxygenation, coastal ecosystems and anthropogenic activities that occur there are left vulnerable. Fish cultured in ocean net pens are increasingly subjected to oxygen stress. Aeration and oxygenation have been utilized to improve oxygen conditions in pond aquaculture; however, their use in open ocean net pens is still in its infancy. In this study, liquid oxygen was distributed through the NetOx Net system within sea cages in a commercial Atlantic salmon (Salmo salar) farm located off Saddle Island, Nova Scotia (Canada). Real-time sensors were used to measure temperature and oxygen before oxygenation, between oxygenation and the onset of de-stratification due to mixing, and after mixing had resulted in full de-stratification. Oxygenation likely resulted in the upwelling of cold deep water, lowering the cage temperature by similar to 4 degrees C which in turn increased oxygen solubility and decreased fish metabolism (though no significant change in growth was observed); these factors resulted in an overall increase in oxygen concentrations by similar to 1.5 mgL(-1). Following de-stratification, the effects of the oxygenation system were diluted, and mixing due to oceanographic processes dominated the system. As climate change increases hypoxia in coastal regions, where aquaculture practices continue to expand, oxygenation systems will become commonplace. Therefore, it is important to understand whether they will work in an environment that is open to other elements.