MICROBIAL MANAGEMENT
Active microbiome management Tom Scrope, Nova Q Ltd. How Recirculating Aquaculture System (RAS) managers can get the most out of their biofilter microbiome.
Active Microbiome Management (regularly adding functional bacteria) should be a part of every RAS farmer’s toolkit.
Why RAS? Recirculating Aquaculture Systems (RAS) can help make aquaculture more sustainable – whether in the much-hyped full-grow out systems or for hatchery, smolt, and now post-smolt production of Atlantic Salmon. Not only do RAS have a low direct environmental impact (especially if renewable power sources are available), but they provide optimal growing conditions. They can reduce mortality and improve feed conversion ratios, reducing the overall emissions per kilo produced. Improvements that can make RAS more efficient and reliable will play a key role in making the aquaculture industry more environmentally sustainable. The challenge RAS aquaculture, though, is not just about farming fish, but the bacteria of the biofilter too. RAS managers recognize that bacteria are crucial to operating a RAS. But as long as adequate nitrification kicks in following “seeding”, most producers are inclined to leave the biofilter “well alone” for fear of disturbing the delicate balance.
Hatchery Feed & Management Vol 9 Issue 2 2021
While other aspects of RAS are being continuously improved – from genetics to system engineering – the functionality of the bacteria in RAS has not been optimized in the same way. To do things better, by definition, we need to do them differently. This lack of innovation has led to problems currently facing RAS sites: • Inefficient nitrification, including nitrite spikes. • Slow and unpredictable restarts – particularly problematic for sites with short timescales before the introduction of fish to the system (e.g. research sites). • Hydrogen sulphide (H₂S) spikes caused by sulphatereducing bacteria being able to establish themselves in the system. • Off-flavor compounds (OFCs) in grow-out RAS reducing the value of stock and requiring expensive and inefficient “purging” to remove. Advances in the last few years in sequencing technology (especially 16S rRNA sequencing) need to be combined with innovative tools to positively influence the microbiome and solve the problems identified above. Some of these tools will involve a more considered use of inputs (e.g. feed) that impact the microbiome.