Influence of dietary C: N: P ratios on Nile tilapia Oreochromis niloticus growth performance and formation of water biotic communities within a biofloc system containment

The present study conducted to evaluate the impact of dietary C: N: P ratios on Nile tilapia, growth induces in biofloc system and formation of water biotic communities. Five isonitrogenous, 30% crude protein and isocaloric 23.35 MJ/kg gross energy were formulated. Diets were equal but with variation of mono ammonium phosphate, NH₄H₂PO₄ levels to obtain different Carbon/Nitrogen/ Phosphorus (C/N/P) dietary ratios. The basal diet had no NH₄H₂PO₄ added (Co) and contain 12:1 N/P ratio. Diets 2–5 each contained NH₄H₂PO₄ at levels of 1.2 (NP10), 3.3 (NP8), 6.8 (NP6) and 13.7 (NP4) g/kg diet, respectively to provide 10:1, 8:1, 6:1 and 4:1 N/P ratios, respectively. Phytoplankton was collected every two weeks during 70 days using 10 L water samples that were sieved via a 10 µm mesh plankton net. The result revealed that the highest growth performance parameters, best nutrients utilization include FCR and PER values were recorded for Nile tilapia fed NP10 diet compared to control treatment. The poorest FCR value was recorded for fish fed the NP6 diet. The phytoplankton community increased with the increasing of dietary phosphate level associated with increasing N: P ratios. On the vice versa, zooplankton showed a remarkable decrease with the increase of phosphate concentrations. The density of aerobic plate count, total Diazotroph, spore forming Diazotroph and lactic acid bacteria increased as the N/P ratio increased to 8:1. The present findings revealed that the fish in the biofloc groups had the best performance and nutrients utilization than the basal diet. However, the positive impacts of BFT technology on growth and feed utilization efficiency of Nile tilapia have been stated.