The total number of Oligochaeta (means±SD) was significantly (p < 0.05) decreased in sumithion low dose (94±14 individualsper m2) and high dose (90±19 individuals per m2), compared to control (192±31 individuals per m2). The Tukey’s post hoc testfurther indicated that there was no difference between sumithionhigh and low doses. The density decreased sharply at the beginning and end of the experimental period in ponds treated with sumithion,whereas density consistently increased in ponds without sumithion (Fig. 2). Oligochaeta contributed 40–44% to total number
of invertebrates depending on the treatments, of which themost dominant genus was Tubifex which accounted for half of the
Oligochaeta abundance (Fig. 1).