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

Area of Science:

• Aquatic Microbiology
• Environmental Biotechnology
• Aquaculture Systems

Background:

• Recirculating aquaculture systems (RAS) require efficient nitrogen cycling for water quality management.
• Low temperatures pose challenges for microbial nitrification processes in RAS.
• Sustainable aquaculture practices are crucial for minimizing environmental impact.

Purpose of the Study:

• To develop and characterize ammonia- and nitrite-oxidizing bacterial communities for low-temperature RAS.
• To establish a functional nitrification system capable of efficiently processing ammonia at 15°C.
• To assess the system's efficacy in supporting cold-water fish rearing and managing nitrogenous waste.

Main Methods:

• Cultivation of distinct ammonia- and nitrite-oxidizing bacterial communities using batch cultures and inorganic media.
• Development of a closed recirculating culture system with enrichment for ammonia-oxidizing bacteria.
• Amplicon sequencing to identify key bacterial groups (Nitrosomonadaceae, Nitrospirales) involved in nitrification.
• Introduction of the bacterial community into tanks for fish rearing (Oryzias latipes var. himedaka, Lefua echigonia) at 15°C.
• Monitoring of ammonia, nitrite, and nitrate levels, with integration of Epipremnum aureum (Pothos) to manage nitrate accumulation.

Main Results:

• A bacterial community efficiently nitrifying 1 mM ammonia within 1 day at 15°C was successfully developed.
• Nitrosomonadaceae and Nitrospirales were identified as the primary bacterial groups responsible for ammonia and nitrite oxidation.
• The system demonstrated effective removal of ammonia and nitrite during the rearing of cold-water fish species.
• Nitrate accumulation was observed but effectively mitigated by the addition of Epipremnum aureum.

Conclusions:

• A robust nitrification system for low-temperature closed recirculating aquaculture was established.
• The developed bacterial community and system design offer a sustainable solution for cold-water fish farming.
• Integration of aquatic plants can further enhance water quality management in RAS by addressing nitrate buildup.