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Penaeus monodon (12.13+/-1.14 g) exposed individually to six different nitrite and nitrate regimes (0.002, 0.36 and 1.46 mM nitrite combined with 0.005 and 7.32 mM nitrate), at a salinity of 25 ppt, were examined for hemolymph nitrogenous compounds and whole shrimp's nitrogen excretions after 24 h. Nitrogen excretion increased directly with ambient nitrite and nitrate. Hemolymph nitrite, nitrate, urea and uric acid levels increased, while hemolymph ammonia, oxyhemocyanin and protein were inversely related to ambient nitrite. Exposure of P. monodon to elevated nitrite in the presence of 7.32 mM nitrate did not alter hemolymph nitrite, ammonia, uric acid, oxyhemocyanin and protein levels, but caused an increase in hemolymph nitrate and a decrease in hemolymph urea as compared to exposure to elevated nitrite only. Following exposure to elevated nitrite, nitrite was oxidized to nitrate and P. monodon showed uricogenesis and uricolysis. The shrimp also used strategies to avoid joint toxicities of nitrite and metabolic ammonia by removing ammonia or reducing ammonia production under the stress of elevated nitrite.

Abstract: Ammonia and nitrite are the most common toxic nitrogenous compounds in aquaculture ponds. We evaluated the effects of a combined treatment with these two compounds on the hemolymph acid–base balance, electrolytes and oxyhemocyanin content in kuruma shrimp, (Marsupenaeus japonicus). The shrimp (6.37±1.29g) were individually exposed to 9 different ammonia and nitrite regimes {ammonia at 0 (control), 0.39, and 1.49mM combined with nitrite at 0 (control), 0.38, and 1.49mM} in a 30‰ saline solution at 22°C. Hemolymph oxyhemocyanin (OxyHc), protein content, acid–base balance, osmolality, and electrolyte levels were measured in treated shrimp after 48h of treatment. Hemolymph OxyHc, protein content, the OxyHc/protein ratio, pH, pCO2, HCO3 −, TCO2, OH−/H+, osmolality, and Cl−, Na+, K+, Ca2+, and Mg2+ levels were inversely related to the dose of ammonia and nitrite. However, hemolymph pO2 levels directly increased with the ammonia and nitrite concentrations. Following exposure to 1.49mM ammonia+1.49mM nitrite, the hemolymph pO2 increased by 89.5%, whereas the hemolymph OxyHc, protein content, OxyHc/protein ratio, pH, pCO2, HCO3 −, TCO2, OH−/H+, osmolality, Cl−, and Na+ decreased by 51.2, 28.2, 34.9, 2.9, 51.1, 71.5, 70.8, 42.8, 4.9, 32.1, and 38.6%, respectively, compared with control shrimp. Combined ammonia and nitrite stress may therefore exert a synergistic effect on shrimp relative to the stress induced by ammonia or nitrite alone. [Copyright &y& Elsevier]