Accumulations of nitrite and nitrate in the tissues of Penaeus monodon exposed to a combined environment of elevated nitrite and nitrate

Penaeus monodon (11.86 +/- 0.63 g) exposed individually to six different nitrite and nitrate regimes [nitrite at 0.002 (control), 0.360, and 1.455 mM combined with nitrate at 0.005 (control) and 7.275 mM] in 25 ppt sea water were examined for the nitrite and nitrate concentrations in tissues and nitrite uptake and nitrate uptake after 24 h in 25.3degreesC. In P. monodon following exposure to 1.455 mM nitrite only, nitrite levels increased by factors of 0.33, 1.05, 1.36, 1.79, 2.10, 2.16, 2.21, and 3.58 in muscle, hepatopancreas, gill, foregut, hemolymph, heart, eyestalk, and mid-ut, respectively, over the ancient nitrite level. In P. monodon, following exposure to combined solutions of 1.455 nM nitrite and 7.275 mM nitrate, nitrite levels were factors of 0.34, 1.05, 1.44, 1.86, 2.21, 2.30, 2.67, and 3.83 in muscle, hepatopancreas, gill, foregut, heart, hemolymph, eyestalk, and midgut, respectively, over the ambient nitrite levels, whereas nitrate levels were factors of 0.06, 0.11. 0.27, 0.29, 0.45, 0.51, 0.57, and 0.61 in muscle, hepatopancreas. foregut, heart, hemolymph, gill, midgut, and eyestalk, respectively, over the ambient nitrate levels. It is concluded that incorporation of nitrite is converted to nitrate in midgut, heart, hemolymph, foregut, and eyestalk, whereas incorporation of nitrate in tissues is converted to nitrite and accumulated in eyestalk when P. monodon are exposed to combined nitrite and nitrate environments.