LAUSR

A 25-week experiment was conducted to investigate the changes in the microeukaryote community (MEC) and nutritional composition of the biofloc during Nile tilapia culture in water-reusing biofloc systems. The study evaluated two treatments: tilapia culture in biofloc (TB) and tilapia culture in biofloc with reuse water (RWTB). Each of the treatments was evaluated using a main culture tank (3 m3) and three experimental tanks (0.2 m3). The biofloc samples were revised with an inverted microscope and the groups of microorganisms and genera of the MEC were recorded. Total abundance of microorganisms (TAM), number of accumulated genera, ecological indices and water quality were evaluated. The MEC of both treatments consisted of microalgae, ciliates, flagellates, amoebas, rotifers, nematodes and annelids; the number of accumulated genera and TAM in RWTB (74 genera, 161.52 ± 80.60 org mL−1) was significantly greater than in TB (63 genera, 139.54 ± 81.39 org mL−1). The TAM in TB and RWTB varied in relation to the temperature, sedimentable solids, NH4-N and NH3-N. The dominance index observed in the RWTB group (0.59) was statistically greater than in the TB group (0.57) during the first 2 weeks of the study. The nutritional composition of the biofloc varied with time; at the end of the study, an increase in the percentage of protein (47%) and a reduction in the percentage of lipids (2%) was observed when compared with values recorded at the beginning of the study. The results suggest that both the richness and TAM of the MEC increase in water-reusing biofloc systems and that the biochemical constitution of the microorganisms which constitute the MEC affects the proximal composition of the biofloc.