| Summary: | Recirculating aquaculture systems (RAS) for fish culture have been used for more than three decades. The interest in RAS is due to their have advantages such as greatly reduced land and water requirements in places where the water resources are limited; but the RAS have also disadvantages like the deterioration of the water quality if the water treatment processes within the system are not controlled properly. The water quality problems in RAS were associated with low DO and high fish waste metabolite levels in the culture water. The objective of this study was to compare water quality in a RAS with water quality in a Limited Reuse System (LRS) for Arctic charr culture taking into account the oxygen demands of the fish; the metabolites production by the fish; the removal of CO2 by the aerators, the removal of ammonia by the biofilter and the removal of waste products in the reuse water. The experiment was conducted in Verid, the Aquaculture Research Facilities of Holar University College, Iceland, during 4 weeks and two different systems were compared during the experiment: a RAS with a biofilter and a LRS. The results of this study indicated that the water quality parameters in both systems were well within the acceptable levels for Arctic charr culture and the water quality was better in the LRS than in the RAS; was demonstrated the important role of the biofilter unit in the RAS and the necessity to control all the water treatment processes within the system, specially when the RAS are using sand filters as one of water treatment components of the system. Department of Aquaculture and Fish Biology. Holar University College, Sauðárkrókur, Iceland. Arctic charr; Recirculating Aquaculture Systems
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