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Nitrite is an intermediate product in bacterial nitrification and denitrification processes in the nitrogen cycle in ecosystems. The concentration of nitrite in natural waters is usually low (µmol/l). However, elevated concentrations of nitrite occur in water receiving nitrogenous wastes, in hypoxic environments or in effluents from industries pro-ducing metal, dyes, and celluloid (Pitter, 1999). In aquaculture, high levels of nitrite up to 2 mmol/l (Avnimelech et al., 1986) can be found causing sev-er health deterioration and even mass mortality of fish (Dvorak, 2004; Svobodova et al., 2005a). Nitrite problems are typically more likely in closed inten-sive culture systems due to insufficient, inefficient or malfunctioning filtration systems removing waste ammonia from water by means of nitrification. Nitrite is actively taken up across the gills and accumulates in plasma, gills, liver, brain and mus-cle (Bath and Eddy, 1980; Margiocco et al., 1983; Gisbert et al., 2004). Nitrite subsequently enters tis-The ability of recovery in common carp after nitrite poisonin