Aquaculture needs specific conditions because fish have well-defined threshold water quality parameters within which they can thrive and grow optimally. However, the use of surface waters for fish production may threaten water ecosystems to which water from fish farms is discharged. The aim of this study was to evaluate the effect of rainbow trout production in a cascade flow technology on the water quality management in a fish farm. The research aim was to collect data in order to prevent contamination of natural water bodies by water discharged from fish ponds. The trout farm selected for the study is located in northern Poland. It has four concrete fish ponds, which are continually supplied with water spring water, flowing in a cascade. Spent water, prior to being discharged from the farm, is pre-treated by flowing through a treatment ditch. The study showed that as a result of flowing through the fish ponds, the quality of water deteriorated down to the lowest class on a five-degree scale (WQICCME), i.e. it was denoted as poor quality. However, it was evidenced that changes in the quality parameters of water after passing through ponds A and B were not large, whereas a more considerable decline in the water quality occurred once it had passed through ponds C and D. The research did not confirm the intended positive influence of a 450-meter-long treatment ditch on the quality of water discharged from the fish farm. Thus, it was demonstrated that water discharged from the fish ponds, despite the implemented system for its pretreatment, creates a risk of polluting water in the receiving water body.  

25.2.2020