Development of a nitrifying bacterial community for a low temperature recirculating aquaculture system.

Two separate ammonia- and nitrite-oxidizing bacterial communities were developed to operate in a low temperature closed recirculating aquaculture system. These communities were cultivated via batch culture using an inorganic nutrient medium containing ammonia or nitrite. Subsequently, a unique closed recirculating culture system was developed, and enrichment culture was performed in an inorganic nutrient medium containing 1 mM ammonia. Through this approach, a bacterial community was developed that can efficiently nitrify 1 mM ammonia within 1 day at 15 °C. Amplicon sequencing revealed Nitrosomonadaceae and Nitrospirales, were the key groups responsible for ammonia and nitrite oxidation. The bacterial community was introduced into microbial tanks for the rearing of Oryzias latipes var. himedaka and Lefua echigonia (Hotokedojo) at 15 °C, where regular measurements confirmed the effective removal of ammonia and nitrite. However, nitrate accumulation occurred, which was mitigated by the introduction of Epipremnum aureum (Pothos) into the tank. This system provides a sustainable solution for the closed recirculating aquaculture of cold-water fish species.