Evaluating Fertilizer Application Rates for Giant Gourami, Osphronemus goramy, Ponds

Abstract

Twelve, 400-m 2 earthen ponds at Walailak University, Thailand, were used to investigate the effects of fertilizer application rates on water quality, bottom soil, and production of giant gourami, Osphronemus goramy .F ertilizer rates of 0, 6, 9, and 12 kg Np lus 0, 3, 4.5, and 6 kg P 2O5 /ha (N:P2O5 = 2:1) applied at 3-wk intervals were replicated three times in a completely randomized design. Ammonium phosphate and ammonium sulfate were sources of nitrogen and phosphorus. Fish averaged 8.8 g and were stocked at 1 fish/m 2 . The highest final weight, growth rate, and net production of giant gourami were achieved with 9 kg N plus 4.5 kg P2O5/ha. Chlorophyll a concentration was correlated with total nitrogen concentration (R2 = 0.574; P< 0.05) and total phosphorus concentration (R2 = 0.600, P< 0.05). Fish production and chlorophyll a concentration were also correlated (0.826; P< 0.05). Chlorophyll a concentration and fish production declined at total hardness concentrations above about 50 mg/L ‐ likely from precipitation of fertilizer phosphorus as calcium phosphate. Pond bottom soil properties did not change in relationship to fertilizer rate.