Part of the enriched biofloc suspension was diluted using fresh seawater
to obtain an estimated TSS of 500 mg L−1. This was considered
as the un-sieved biofloc group. The remaining suspension was sieved
over 2 stacked nylon filters of 100 μmand48μmmeshsize, respectively,
to obtain the N100 μm, 48–100 μm, and b48 μm floc size groups. A subsample
of the enriched floc suspension was brought on the sieves and
gently swirled to avoid inducing disintegration of the flocs until all suspension
passed through. The flocs that did not pass the filters (N100 μm
group and 48 μm–100 μm group) were gently transferred to fresh seawater
before the next volume of biofloc suspension was sieved. Finally,
all floc size classes were resuspended in seawater at an estimated TSS
concentration of 500 mg L−1 and aerated for 1 h resulting in 4 different
batches of flocs produced with different sizes: original un-sieved flocs,
flocs which passed through the 48 μm sieve (b48 μm), flocs whichpassed through the 100 μm but not the 48 μm sieve (48 μm–100 μm),
and flocs which did not pass the 100 μm sieve (N100 μm). Five samples
from each batch were collected for total suspended solid (TSS) measurement
to determine initial TSS. In addition, duplicate samples of
each biofloc suspensionwere analyzed in terms of particle size distribution,
nutritional composition, total nitrogen content and 15N content. To
determine the mass fractions of the b48 μm, 48–100 μm, and N100 μm
floc size groups in the un-sieved biofloc group, 1 L of un-sieved biofloc
suspensionwas fractioned into the respective floc size groups according
to the previously described procedure, and the dry weight of each size
group was determined after drying at 105 °C for 4 h.