Stock solutions of 1000 mg/L NO3–N were prepared weekly by
adding 6.07 g NaNO3 to 1L distilled water. The nominal concentrations
of NO3–N tested were 10, 50 and 100 mg/L, respectively.
Reagent-grade NaNO3 (Sigma, St. Louis, MO) was used to prepare
stock solution. Each stock solution was electronically pipetted
and well-mixed with certain volume of dechlorinated water to
obtain the nominal concentrations, and then added to the aquarium.
Additionally, exposed individuals were kept under the same
experimental conditions (at 18 ± 1 C under a 12 h light: 12 h dark
cycle). In order to maintain the appropriate concentration of NO3–
N and water quality, fifty percent of test solutions volume was
renewed daily and entirely replaced every 48 h. Dead larvae were
removed, and survival were evaluated when renewing the
solutions.