Recovery of Penaeus monodon from functional anaemia after exposure to sublethal concentration of nitrite at different pH levels

Abstract

Tiger shrimp Penaeus monodon (14.79±0.19 g) which had been exposed individually to 0.72 mM nitrite at pH 6.8, 8.2 and 9.8 after 3, 6, 12, 24 and 48 h were examined for the water nitrite concentration, hemolymph nitrite, oxyhemocyanin, protein and osmolality levels. Same parameters were examined for shrimp depurated in nitrite-free water after 3, 6, 12 and 24 h following 48 h exposure to nitrite. In the nitrite-exposed test, nitrite influx, hemolymph nitrite and osmotic differential (medium osmolality — hemolymph osmolality) increased with exposure time, and were higher at pH 6.8, whereas water nitrite concentration, oxyhemocyanin, protein, ratio of oxyhemocyanin to protein and hemolymph osmolality decreased with exposure time and were lower at pH 6.8. In the depuration test, water nitrite concentration increased with depuration time, and was higher at pH 6.8, whereas, hemolymph oxyhemocyanin, ratio of oxyhemocyanin to protein and hemolymph osmolality increased with depuration time and were higher at pH 9.8. Hemolymph nitrite decreased with depuration time, and was 2.52, 2.19 and 0.24 μmol ml −1 after 6 h at pH 6.8, 8.2 and 9.8, respectively. Nitrite entry is considered to occur mainly via the form of nitrous acid (HNO 2) in water uptake. The fact that the hemolymph nitrite decreased to non-detectable level with 72–88% recovery of oxyhemocyanin after 24 h depuration suggests an occurrence of reductase for nitrite-exposed shrimps.