Assessment of the effects of the insecticide methyl parathion on Nile tilapia (Oreochromis niloticus) fingerling in a small-scale rice-fish culture, and on freshwater prawn juvenile (Macrobrachium rosenbergii) in tanks
1992
Phuong, Thanh Nguyen
Acute bioassay was conducted to determine the toxicity of methyl parathion to Nile tilapia (Oreochromis niloticus) fingerlings (1.55 g in weight) and prawn post-larvae (Macrobrachium rosenbergii) (0.015 g in weight). The LC50 at 24 and 96 hour exposure to methyl parathion was 6.76 and 5.78 mg a.i./l for tilapia and 0.41 and 0.041 micro g a.i./l for prawn, respectively. The post-larvae stage of Macrobrachium rosenbergii was more sensitive to methyl parathion than tilapia fingerling. An experiment was set up in a rice field to assess the effects of methyl parathion on tilapia fingerling (1.42 g in weight) in a small-scale rice-fish culture system. Methyl parathion was applied at different rates (0.24, 0.48, 2.4 and 4.8 mg a.i./l). At an application rate of 4.8 mg methyl parathion per liter, survival and biomass production of tilapia was significantly reduced (P0.01). No effects were detected at 0.48 mg/l or less. Fish yield was highest in control, 0.24 and 0.48 mg/ treatment, at an equivalent of 634.1, 587.4 and 415.4 kg/ha after 70 days stocking, respectively. Increase of rice yield by 13 to 30 % was recorded in all treatments with fish compared to rice fields without fish. Long-term effect of methyl parathion to Macrobrachium post-larvae (0.12 g in weight) was investigated in a concrete-tank. Survival and biomass production of prawn were significant reduce (P0.01) at a 4.25 and 8.5 micro g a.i./L, applied every 10 days. No negative impact of methyl parathion to prawn at 0.21, 0.42 and 2.13 micro g/l, was measured in terms of survival, biomass production and growth rate. Prawn had significantly better survival rate and yield at methyl parathion treatment of 0.213 and 0.425 micro g/l (P0.01).
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This bibliographic record has been provided by Thai National AGRIS Centre, Kasetsart University
