Individuals were allowed to develop to stage G26 before chronic
toxicity testing (Gosner, 1960). For the study of developmental
changes in metamorphosis, larvae at stage G26 were randomly
selected and transferred into aquariums (50 cm 20 cm 10 cm)
with certain nitrate concentrations in 5 L dechlorinated water
(well-exposed). The experimental control groups exposed to 5 L
dechlorinated water only. Tests consisted of 50 individuals per
each container with three replicate containers per exposure concentration
including controls. Larvae were offered boiled vegetables
during exposure to NaNO3.