This study aimed  to estimate the effect of biofloc technology (BFT) implementation on water quality and production performance of Nile tilapia (Oreochromis niloticus) using different concentrations of ammonia and attempt for treatment of excess ammonia by biofloc system with fixed temperature, pH and dissolved oxygen. The improvement and organization of phytoplankton communities in each case was monitored. The hematological and histological alterations of studied fish were also noticeable. Phytoplankton communities developed in this study were dominated by Chlorophyceae followed by Cyanophyceae, Bacillariophyceae and Euglenophyceae.
The collected fish were divided into five groups; the first group was left as the control, the second and third groups were supplemented with ammonia (0.25 LC₅₀, 0.50 LC₅₀) and the fourth and fifth groups were cultured under biofloc system (0.25 LC₅₀, 0.50 LC₅₀). The results revealed that the phytoplankton used in the biofloc system gradually converted ammonia into nitrate. Hematological studies revealed that the studied biochemical parameters of blood obtained from fish cultured under biofloc system were very close to that of the control. Also, histological studies showed that fish cultured under biofloc system appeared close to recovery and similar to that obtained from control. In conclusion, phytoplankton in the biofloc system improves water quality and production performance of cultured fish by enhancing nitrification and transformation, of ammonia (toxic) into nitrate (non-toxic).