Effects of three fertilization treatments on water quality, zooplankton, and striped bass fingerling production in plastic-lined ponds

Three pond fertilization treatments were compared in plastic-lined ponds to determine their effects on water quality, zooplankton, and production of fingerling striped bass Morone saxatilis. Treatment 1 used only alfalfa meal (100-200 kg/ha); treatment 2 used alfalfa meal (100-150 kg/ha) followed by ammonium nitrate and phosphoric acid after 24 h to maintain 210-mu g N/L and 30-mu g P/L target levels; and treatment 3 used alfalfa meal (100-150 kg/ha) followed by ammonium nitrate and phosphoric acid after 24 h to maintain 300-mu g N/L and 20-mu g P/L target levels. Treatment 1 promoted the most desirable water quality, including moderate pH and was most conducive to survival and production of fingerling striped bass. Mean pH values were 8.3 for treatment 1, 8.5 for treatment 2, and 8.6 for treatment 3; differences among treatments were significant (P less than or equal to 0.05). Mean adult crustacean densities were lowest in treatment 1 ponds and highest in treatment 3 ponds; however, mean total zooplankton densities were similar among treatments. Mean adult crustacean density correlated negatively with survival (r(2) = 0.74; P = 0.003) and positively with growth of fingerling striped bass (r(2) = 0.90; P = 0.0001), indicating that fish grazing pressure was fish density-dependent and that adult crustaceans were important food items for striped bass. Mean striped bass survival at harvest was 86.7% for treatment 1, 53.1% for treatment 2, and 36.4% for treatment 3; however, production of striped bass fingerlings (range, 160.7-173.5 kg/ha) was similar among treatments. Growth of striped bass was negatively correlated with survival (r(2) = 0.86; P = 0.0003), suggesting that growth was density-dependent and food was probably limiting in ponds with high survival rates. Survival was negatively correlated with pH (r(2) = 0.77, P = 0.002), suggesting that alkalinity could be a source of fish mortality.