The effects of temperature and salinity on phosphate levels in two euryhaline crustacean species

Abstract Total phoshate, inorganic phosphate and organic (phospholipid) phosphate concentrations were determined in the blood of Carcinus maenas and in whole-animal homogenates of Penaeus japonicus acclimatized to various salinities and a high or a low temperature. In the blood of Carcinus , total and inorganic P concentrations range between 1.0 and 4.5 mmol · l −1 ; the amount of phospholipids is negligeable. The higher values were found at more extreme salinities. Low temperature is associated with low phosphate concentrations, particularly at intermediate salinities. Total P concentrations in Penaeus homogenates range between 10 and 60 mmol · 1 −1 ; phospholipid concentrations range between zero and 50 mmol · 1 −1 . The higher values are again found at the extreme salinities. Inorganic P concentrations are almost constant — ca 10 mmol · 1 −1 . No apparent effect of temperature on phosphate concentrations was observed. The results show clearly that osmotic stress influences severely the phosphate metabolism of the two species studied. Both species are able to accumulate phosphate at all experimental temperature/salinity combinations used, even when deprived of food. At extreme salinities, large quantities of phosphate are accumulated and converted to organic P compounds, most likely as phospholipids associated with the cell membranes. These effects of osmotic conditions in phosphate metabolism may offer an explanation for the effect of Ca ++ on membrane permeability as the regulation of both ions may be strongly interrelated, often under hormonal control.