February 15-18, 2009 Washington State Convention Center Seattle ...

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MONITORING TOOLS FOR CHARACTERIZING AND MANAGING MICROBIAL BIOFLOC
COMMUNITIES IN SUPERINTENSIVE ZERO-EXCHANGE SHRIMP CULTURE SYSTEMS
John W. Leffler*, Alisha Lawson, Andrew Ray, Gloria Seaborn, Andrew Shuler, Beth Thomas, Jesus Venero,
Luis Vinatea, and Craig L. Browdy
South Carolina Department of Natural Resources
Marine Resources Research Institute
217 Fort Johnson Road
Charleston, SC 29412 USA
Lefflerj@dnr.sc.gov
Superintensive, zero-exchange shrimp culture technologies demonstrate great potential for commercialization. Such systems
rely on the structure and function of a rich microbial “biofloc” community to process nitrogenous wastes, stabilize water
chemistry, and provide supplemental nutrition to the shrimp. However biofloc communities differ and may achieve these goals
to varying degrees. We have evaluated several for their usefulness for characterizing these communities and their potential
to assist in biofloc management protocols. These methods have been employed in both large outdoor tanks and greenhouse
raceways.
Traditional membrane dissolved oxygen sensors foul within hours of immersion in these biofloc systems and are of little use for
continuous monitoring and for operating automated aeration or emergency liquid oxygen systems. A YSI ® optical DO sensor
and a YSI ® pulsed polarographic DO sensor, both equipped with automated wipers, were mounted on the same YSI ® 6600 sonde
and deployed in a mature biofloc community for 52 consecutive days without maintenance. Both sensors performed equally
well and data obtained from them had considerably less random variability than readings conducted twice daily by a technician
using a handheld DO meter. Another sonde equipped with YSI ® phycocyanin and phycoerythrin Blue-green Algae sensors was
deployed in a raceway for 28 days to monitor cyanobacterial abundance. Although the system’s salinity was 35 ppt, the “freshwater”
phycocyanin sensor yielded data with less random noise and provided more accurate cyanobacterial estimates compared
to visual cell counts conducted with an epifluorescent inverted microscope equipped with cyanobacterial specific filters.
Several techniques were employed to better characterize the structure and activity of the microbial biofloc community. These
included direct microscopic observations using a scaled ranking system, and epifluorescent microscopy coupled with computer-aided
image analysis to quantify relative levels of algae, cyanobacteria, and heterotrophic bacteria. Tracking relative
bacterial abundance by quantification of fatty acids characteristic of bacteria (branched and odd chains) proved very effective.
Total community metabolism and suspended microbial community metabolism were measured in situ and in a specially designed
rotating incubator. Shrimp respiration was also estimated from lab respirometry. These techniques estimated that the
microbial biofloc community was responsible for approximately 80% of the total system oxygen demand. Critical evaluation
of these measurement techniques found some not to be useful, some appropriate in a research setting to develop protocols, and
some suitable for routine use by producers to improve system management.