Effects of nitrite exposure on the hemolymph electrolyte, respiratory protein and free amino acid levels and water content of Penaeus japonicus

Penaeus japonicus which bad been exposed individually for 3, 6, 12, 24 and 48 h to 0.001 (control), 0.07, 0.36, 0.72 and 1.43 mM nitrite at 30 ppt of salinity were examined for hemolymph electrolyte, oxyhemocyanin, protein, free amino acid (FAA) and urea levels and whole shrimp's nitrite uptake and ammonia excretion. Hemolymph oxyhemocyanin, protein, FAA, osmolality, Cl- and Na+ levels were inversely related to ambient nitrite and exposure time. However, hemolymph urea level, osmotic differential (medium osmolality - hemolymph osmolality), nitrite uptake. ammonia excretion and water content increased directly with ambient nitrite and exposure time. It is suggested that when P. japonicus are exposed to nitrite, water uptake and nitrite uptake result in reductions of hemolymph Cl-, Na+ and protein levels leading to a decrease of hemolymph osmolality. An increase of hemolymph urea and a decrease of arginine may indicate an occurrence of ureogenesis for the intracellular osmoregulation of P. japonicus under nitrite stress. (C) 1998 Elsevier Science B.V. All rights reserved.