Assessment of Fertilizer Application Intervals for Giant Gourami (Osphronemus goramy Lacepede) in Ponds

The experiment was conducted in twelve 400 m2 earthen ponds at Walailak University, Thailand, to investigate the effects of fertilizer application intervals on production performances of giant gourami and pond water quality. Fertilizer applications at 1, 2, 3 and 4-week intervals were replicated three times in a completely randomized design. Ammonium phosphate and ammonium sulfate were used at application rates of 9 kg N plus 4.5 kg P2O5 ha-1 (N:P2O5 = 2:1) as a source of nitrogen and phosphorus. Fish of an average weight of 2.2 ± 0.1 g were stocked at 1 fish/m2. After the 120 day trial was finished, the results showed that the survival rate was not significantly different (p > 0.05) but final weights, growth rates and net productions were significantly different (p < 0.05). Fertilizer applications at 4-week intervals showed the highest (average ± SD) final weights, growth rates and net productions which were 37.6 ± 3.4 g, 0.3 ± 0.03 gd-1 and 330 ± 2.5 kg/ha respectively. However, most water quality parameters were not significantly different (p > 0.05) and were in the range for optimal growth of fish. In addition, the result from regression analysis showed that fertilizer application intervals gave a high positive correlation with fish productions (r = 0.76, p < 0.01). In conclusion, the results suggest that fertilizer applications at 4-week intervals could have practical use in the giant gourami ponds to produce fish ranging from 2.2 ± 0.1 - 37.6 ± 3.4 g size during the 120 day production.