WATER QUALITY UNDER DIFFERENT POND MANAGEMENT

Temperature, visibility, pH, dissolved oxygen, total hardness, to­tal alkalinity, orthophosphate-phosphorus, chlorophyll-a and phytoplank­ton-zooplanton abundance were measured frequently in polyculture ponds, of which two ponds were fertilized with urea and superphosphate (1st treatment); two ponds were fertilized with urea, superphosphate and supplied with supplemental feed (17% protein) at 3% of fish bio­mass (2nd treatment), and two ponds were used as control. The experi­ment extended from September 1992 to February 1993 for two sea­sons, fall and winter. Data of the two seasons showed that the average concentration of PO4-P and NH4-N decreased, while, NO3-N increased from fall to winter in all treatments. No treatment effect was observed for nitrate (NO3-N), ammonia (NH4-N) in the chemical fertilizer and con­trol treatments. Phytoplankton and zooplankton abundance were signifi­cantly different (P<0.05) between treatments, the hightes abundance was in 1st treatment. Net fish production were 89.2, 599 and 1079 kg/ feddan in control, 1st and 2nd treatments, respectively.