Micro particles and microbial activity in Danish recirculating rainbow trout (Oncorhynchus mykiss) farms

Abstract Increasing intensities of water reuse in recirculating aquaculture systems (RAS) lead to a build-up of micro particles ( Oncorhynchus mykiss ) in a total of 20 separate RAS units. Micro particle numbers and size distribution, bacterial activity, and inorganic and organic nutrient concentrations were analysed. Micro particle numbers ranged between 6.0·10 4 – 7.4·10 5  ml −1 and large variations were found between seemingly similarly operated RAS units within the same farm. There was a strong, positive correlation (p