ARS | Publication request: A submersible magnetic stirrer for use in measuring photosynthesis in a biofloc technology production system

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 25, 2012
Publication Date: June 26, 2012
Citation: Green, B.W., O'Neal Jr, E.G. 2012. A submersible magnetic stirrer for use in measuring photosynthesis in a biofloc technology production system. North American Journal of Aquaculture. 74:347-351.

Interpretive Summary: Fish can be raised super-intensively using what is known as the biofloc technology production system. In this production system, fish are stocked and fed at rates that exceed traditional pond culture rates by a factor of 10 or more. An assemblage of algae and bacteria and associated particulate organic matter, known collectively as the biofloc, are suspended and in constant motion throughout the water column because of the water currents generated by continuous aeration of the water. Both the algae and bacteria consume nutrients excreted by the fed fish. Primary productivity is a measure of how much algae is produced as a result of these nutrients and it is measured by incubating water samples in special bottles that are suspended in the water column during daylight hours. Because the biofloc will settle out of suspension inside these bottles, primary productivity measurements will be inaccurate. In order to overcome this problem, a submersible device is needed to keep the biofloc suspended inside the bottles during incubation. We describe a submersible, air-powered magnetic stirrer that we designed and fabricated from off-the-shelf materials. In tests conducted in a biofloc technology production system, the stirrer successfully maintained the biofloc in suspension inside the bottles throughout the incubation period and allowed for accurate primary productivity measurements.

Technical Abstract: Measuring photosynthesis or primary productivity in biofloc technology production systems is challenging because the biofloc must be maintained in suspension constantly. Photosynthesis can be measured in external incubators designed to keep the biofloc suspended in the biochemical oxygen demand (BOD) bottle, but primary productivity must be measured in the biofloc technology production system culture unit. Therefore, a submersible device is required to keep the biofloc suspended in the BOD bottle. This report details a submersible, air-powered magnetic stirrer that we designed, fabricated from off-the-shelf materials, and tested in biofloc technology production system tanks.