2019

Suurnäkki, Suvi; Pulkkinen, Jani T.; Lindholm-Lehto, Petra C.; Tiirola, Marja; Aalto, Sanni L.

Microbial biofilters control water quality and enable the overall function of recirculation aquaculture systems (RAS). Changes in environmental conditions can affect the abundance and interactions of the diverse microbial populations of the biofilter, affecting nitrification of harmful ammonium and thus fish health. Here, we examined the effect of different application frequencies (0, 1, 2 and 4 times per week) of a common disinfectant, peracetic acid (PAA, applied 1.1 mg l−1 twice per day), on biofilter microbial communities, focusing especially on nitrifying microbial groups and using a high throughput sequencing of 16S rRNA gene and quantitative PCR (qPCR). In addition, we measured biofilter nitrification rates, water quality parameters, and fish performance. Although PAA additions did not significantly change the overall microbial community composition or abundance, the abundance of ammonia-oxidizing bacteria (AOB) and nitrate-oxidizing bacteria (NOB) first decreased at the beginning of the experiment but increased in numbers towards the end of the experiment with frequent PAA applications. PAA application decreased the nitrification rate, but increased the water quality in terms of reduced ammonium levels. PAA application did not significantly affect fish growth, but higher mortality was observed with the highest PAA application level of 4 times per week. These results suggest that when applied before the fish tank, PAA can be used for temporary water quality improvement without disturbing microbial communities. However, the application frequency required for persistent water quality improvement caused increased mortality.