Defining the nitrogen fixation community size, structure and relevancy in Nile tilapia aquaculture pond waters

Nitrogen fixation microbial communities within 3 different intensity Nile tilapia (Oreochromis niloticus) pond water columns were identified and correlated to environmental factors, influencing their summer pond productions in Yi Xing China. The microbial communities encoding the nifH - gene and known to promote plant growth, reduction of pond nitrate leaching and pollution were taxonomically identified to their most probable genera, revealing Azospirillum, Azoarcus, Anaeromyxobacter, Azotobacter, Geobacter, Trichormus, and unclassified_Opitutaceae, as the most dominant. Of the studied environmental factors, ammonium concentrations with the greatest influence on the communities recorded the highest significant differences of 3.18, 1.98 and 3.41 mg/L for the 3 studied ponds. The monthly mean temperatures, dissolved oxygen and pH values were documented and observed to be above pond culture optimal, while the chemical oxygen demand and total organic carbon nutrient content revealed an increment in energy sources within the pond systems. Quantitative analysis of the microbes encoding nifH gene abundances were established as 3.65 x 106, 2.66 x 106 and 3.11 x 106 copies/g wet weights in ponds 1, 2 and 3 respectively. Linear discriminant analysis effect size revealed Chromatiaceae and Thiocapsa as the closest relatives in the three ponds, while the Redundancy analysis tests indicated ammonia nitrogen, total phosphorous and dissolved Oxygen were the most important factors shaping the bacterial communities.