Recirculation and re-use of water by simple means can result in several operational advantages even in extensive systems. Likewise, using some of the ideas and technologies from intensive recirculation, modified for less intensive use, can add important benefits to fish farming in semi-intensive systems.

By applying even lower degrees of recirculation (e.g. 50-90%), regulation and control of important production parameters like oxygen and carbon dioxide content, ammonia and organic matter content, pH and temperature can be obtained. At the same time, the need for intake of fresh water can be reduced by a factor 2-10, with beneficial effects to smaller watercourses.

Due to the lower degree of recirculation, simple and “home-made” installations can often be used, reducing the investment costs. Nevertheless, R&D within the field is much needed in order to at one hand reduce investment and running costs, while at the other hand still securing permanent operation.

Per Bovbjerg Pedersen, M.Sc. is a researcher at the aquaculture group of Danish Institute for Fisheries Research in Hirtshals. He has been working within the field of aquaculture for more than 15 years, addressing practical and developmental as well as scientific issues. He has designed, build and operated recirculation systems for many purposes through-out the years.

Contact details: Danish Institute of Fisheries Research, North Sea Centre, DK-9850 Hirtshals, Denmark. E-mail: pbp@dfu.min.dk