This study was carried out at Wady El-Ryan, Fayoum Governorate, Egypt to evaluate the influence of humic acid on enrichment of plankton community, water quality, growth performance and pond productivity of Nile tilapia. Eight earthen ponds of a total area of two feddan were used. These fish ponds were divided into four treatments; two replicates per each as the first treatment ponds (T1 and T2) were stocked with Nile tilapia fry 14000 fish/Fadden. The second ponds (T3 and T4) were stocked with 28000 fish/Fadden. T2 and T4 treatment ponds received only supplemental feed at a rate of 3% of body weight (bw), while T1 and T3 were treated with humic acid at a rate of 3 Kg/ Feddan during the preparation of the ponds, then they received a supplemental feed adding on it 1.5 Kg of humic acid/ ton feed. Comparison between treatments showed that there were no significant differences (p> 0.05) in water temperature, salinity, total hardness and total alkalinity. Dissolved oxygen, orthophosphate, Chlorophyll "a", concentrations in T1 and T3 ponds were significantly higher (p< 0.05) than those of T2 and T4 ponds. Free ammonia, nitrate and nitrite concentrations in T2 and T4 ponds were significantly higher (p< 0.05) than those of T1 and T3 ponds. Secchi disk reading was significantly higher in T4 ponds than that of the other treatment ponds. Phytoplankton and zooplankton abundances were significantly higher in T1 and T3 ponds than those of T2 and T4. The final weight of Nile tilapia was maximized at T1 ponds, while the lowest one was in T4 ponds.
Humic acid; Nile tilapia; Water Quality; Phytoplankton; Zooplankton