Guppy (Poecilia reticulata) was selected to investigate the effects of chlorpyrifos on reproductive performances. Male and female guppy with proven fertility were selected from our own colony and the groups of fish (n = 72/group) were exposed to pre-determined chlorpyrifos concentrations (0.002 μg/l, 2 μg/l) based on the 96-h LC50 for guppy