Hemolymph oxyhemocyanin, protein levels, acid-base balance, and ammonia and urea excretions of Penaeus japonicus exposed to saponin at different salinity levels

Abstract

Penaeus japonicus were exposed individually to 0 (control), 1, 5, 10 and 20 mg l(-1) saponin-sapogenin in 18, 26 and 34 ppt salinity for 24 h. Hemolymph ammonia, urea, oxyhemocyanin, protein levels, hemolymph pH, partial pressure of oxygen (P-O2), partial pressure of carbon dioxide (P-CO2), HCO3-, total carbon dioxide (T-CO2), and whole animal ammonia-N and urea-N excretions were determined. There was an increase in hemolymph urea, with a reduction in hemolymph ammonia and decreases in both ammonia-N and urea-N excretions, when shrimps were exposed to increased ambient saponin. Hemolymph urea also increased with increase of salinity, but hemolymph oxyhemocyanin decreased with increase of salinity and saponin. Hemolymph P-O2 increased directly with saponin, while hemolymph pH, P-CO2, HCO3- and T-CO2 were inversely related to saponin. It is suggested that P. japonicus, following exposure to saponin-sapogenin at 10 mg l(-1) or higher, decreases oxygen affinity of hemocyanin, and causes metabolic product of ammonia and HCO3- to form urea through the ornithine-urea cycle.