2.4. Imaging and identification of microorganisms in biofloc
The 3-D images of bacterial floc were taken using a confocal
microscope (Leica TCS 4PI) on a biweekly basis. Water samples were
collected from one tank in each treatment and processed immediately
for microscopy. Each sample was diluted with pre-filtered water of the
same tank, stained with fluorescence 4′-6-Diamidino-2-phenylindole
(DAPI), and observed and photographed at magnification 10.
Taxonomic composition of other organisms in the water was
studied in three consecutive weeks in the middle of experimental
period. Well-mixed water samples were collected in 30 ml plastic
bottles and the organisms were killed by adding several drops of
Lugol's iodine. One ml sample was placed on the counting chamber of
the Sedgewick Rafter counting cell (S-R cell) and left for several
minutes to allow organisms to settle. Then the organisms on 10
randomly selected fields of the chamber were identified and counted
using magnification of 20–40 of a binocular microscope (Olympus
LH50A). The number was multiplied by 100 to give the results in total
number of organisms per ml water. This counting was repeated three
times in each sample in each tank. The keys used for taxonomic
identification of the microorganisms were Donner (1966), Patterson
and Hedley (1992) and Nuffield Advanced Science (1970).