Joint action of elevated ambient nitrite and nitrate on hemolymph nitrogenous compounds and nitrogen excretion of tiger shrimp Penaeus monodon

Abstract

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.