Changes of osmotic and electrolyte concentrations in the haemolymph of Penaeus japonicus exposed to ambient ammonia

The osmolality and sodium, potassium, calcium, magnesium and chloride concentrations in the haemolymph of Penaeus japonicus individually exposed for 24 h in a salinity of 30 at 25 degrees C to 0.004 (control), 0.076, 0.356, 0.784, and 1.476 mmol/L ammonia-N (molecular ammonia plus ammonium as nitrogen) were examined. The haemolymph osmolality and sodium concentration of shrimps exposed to 0.356 mmol/L ammonia-N, and haemolymph concentrations of sodium, calcium, magnesium and chloride of shrimps exposed to 1.476 mmol/L were significantly lower (P < 0.05) than those in the control animals. It is concluded that P. japonicus is iso-osmotic in control water, and becomes hypo-osmotic to the environment due to significant decreases of haemolymph electrolytes under ammonia stress at concentrations as high as 1.476 mmol/L.