The impact of water exchange rate on the health and performance of rainbow trout Oncorhynchus mykiss in water recirculation aquaculture systems

AbstractA controlled six-month study was conducted in six replicated water recirculation aquaculture systems (WRAS) to assess fish health indicators in relation to high feeding/low flushing conditions. Juvenile rainbow trout (Oncorhynchus mykiss) were stocked in six identical WRAS (1000 fish per system), and were maintained over the study period between 25 kg/m3 (minimum) and 80 kg/m3 (maximum) densities. Three WRAS received a relatively high makeup water exchange rate (2.6%), while three systems received only 0.26% exchange; mean feed loadings of 0.39 and 4.1 kg/day per m3/day of makeup water flow were maintained for the high and low exchange treatments, respectively. At the end of the study period, there were surprisingly no significant (p