| Summary: | Over the last several decades, recirculating aquaculture systems (RAS) have become a viable technology for the production of high-value food-fish. In Norway, for example, many Atlantic salmon smolt farms are now using RAS, and there is increased interest and investment in landbased facilities for the production of larger smolts, post-smolts, and, in some cases, market-size Atlantic salmon. Similar trends are taking shape in other countries, including the United States where multi-million-dollar land-based salmon and trout facilities are being planned and constructed with several already in operation. RAS continuously recycle water through specialized unit processes that recondition the flow to support intensive fish production. Core advantages of RAS include substantial water savings, diminished waste discharge, and increased flexibility for siting facilities near major seafood markets; however, a critical tradeoff is the accumulation of dissolved nutrients, metals, and compounds that can negatively affect fish health and performance in the absence of proper water treatment and system management techniques. Therefore, research that prioritizes assessment of technologies and operational metrics that optimize the RAS environment has been and will continue to be essential for sustainable industry growth. During my 21-year career as a researcher at The Conservation Fund’s Freshwater Institute, I have focused largely on evaluating the suitability of environmental conditions for salmonid production in RAS. Early research sought to identify accumulating water quality variables of concern, followed by studies designed to establish safe water quality thresholds for salmonids, namely nitrate. Assessment of specialized technologies for water quality control was intertwined with these objectives and is now at the forefront of today’s research. As the use of RAS for intensive salmonid production is still a relatively new frontier, novel questions continue to arise and evolve with increasing RAS scale, adoption of new ...
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