A one-month chronic exposure of common carp larvae and embryos to nitrite revealed significant (p < 0.01) differences in total accumulated mortality in fish exposed to 33, 67, and 330 mg/L NO(2)(-) compared with controls. At the highest concentration, all fish died within 8 d of exposure. On the basis of accumulated mortality in the experimental groups, lethal concentrations of nitrite were estimated at 29 d LC50 = 88 mg/L NO(2)(-); lowest-observed-effect concentration (LOEC) = 28 mg/L NO(2)(-); and no-observed-effect concentration (NOEC) = 7 mg/L NO(2)(-). Fulton's condition factor values were significantly lower in fish from all experimental groups compared with controls. By day 12, fish exposed to 33 and 67 mg/L NO(2)(-) had significantly lower mass and total length compared with controls. No significant negative effects of nitrite at the concentrations tested (0.7-330 mg/L NO(2)(-), at 10 mg/L Cl(-)) on hatching or embryo viability were demonstrated, but significant differences in early ontogeny among groups were noted. Fish from all the concentrations showed a dose-related delay in development compared with the controls. Lordosis, kyphosis, scoliosis, and body shortening were observed at all concentrations and in controls, as was yolk sac deformation and edema, eye deformation, and cardiac edema. The incidence of these malformations was positively correlated with nitrite concentration. Histopathology revealed epidermal spongiosis; edema and hyperplasia of the gill epithelium, including hypertrophy and hyperplasia of eosinophilic granular cells (chloride cells); and interstitial edema of skeletal muscle in fish exposed to 67 mg/L NO(2)(-). Similar, but milder, changes were observed at lower nitrite concentrations.