Impacts of fish and pesticide in lowland irrigated rice fields

Abstract

This study examined the effects of fish and pesticide on selected components of the rice-cum-fish farming system using treatments without and with fish and pesticide conducted in two trials (wet and dry seasons). Polyculture of Nile tilapia Oreochromis niloticus and common carp Cyprinus carpio at 104kg/ha (1:1 ratio by weight) was employed.Results revealed some positive and negative impacts of fish and pesticide. Fish polyculture in rice field increased rice grain yield (10%) (P>0.05) in one out of two trials (trial 2). Based on the mean of two trials, the presence of fish decreased oligochaete abundance by 82% (P<0.01) while pesticide effect was positively manifested in increased rice grain yield but reduced oligochaetes (44%) (P<0.05). Fish growth and yield were not significantly affected by pesticide. No significant interaction effect of fish and pesticide were found for rice grain yield and aquatic oligochaetes. Findings on gross primary productivity (GPP) seemed to indicate the stimulating effects of fish and pesticide. Mean GPP from two trials was ten times higher in the pond refuge (2.74-3.42 g carbon m 2 day) than in the rice field (0.27-0.34 g carbon m-2 day-). This suggests the advantage of pond refuge, a contiguous part of rice field, for fish culture in rice-cum-fish system.