Effects of nitrite exposure on acid-base balance, respiratory protein, and ion concentrations of giant freshwater prawn Macrobrachium rosenbergii at low pH

Abstract

Macrobrachium rosenbergii that had been exposed individually for 24 h to 0 (control), 2, 5, 10 mg/L nitrite-N (nitrite as nitrogen) at 4.3 and 7.7 pH levels were examined for hemolymph nitrite-N, oxyhemocyanin, protein, acid-base balance, ion concentrations, and ammonia-N (ammonia as nitrogen) excretion. Hemolymph oxyhemocyanin, protein, pH, HCO3-, TCO2, osmolality, and ion concentrations were inversely related to ambient nitrite-N concentration and were lower at pH 4.3. However, hemolymph nitrite-N, PO2 and Pco(2) levels, and ammonia-N excretion were directly related to ambient nitrite-N, and were higher at pH 4.3. Ambient nitrite-N and pH level interacted to cause changes in hemolymph nitrite-N, oxyhemocyanin, protein, Po-2, and pH levels. It is concluded that for M. rosenbergii following nitrite exposure, the incorporated nitrite causes a decrease of pH and an increase of Po-2 in the hemolymph where it reduces oxyhemocyanin level; disturbs nitrogen excretion, ion regulation, and respiratory gas exchange; and may lead to a decrease of oxygen-carrying capacity, which are affected more at low pH.