ABSTRACT
Non-protein and protein nitrogen fractions of the isopod Sphaeroma rugicauda were measured in animals adapted to 100 and 2% sea water.
The non-protein nitrogen component was reduced in animals acclimatized to the lower salinity.
Free amino acids accounted for 88 and 74% respectively of the non-protein nitrogen in the two salinities.
In 2 % sea water taurine, proline, glycine, alanine and glutamic acid showed the greatest decreases in concentration compared to the levels measured in animals adapted to 100% sea water.
The decrease in total free amino acids of animals acclimatized to 100% sea water and transferred to 2% sea water was measured.
The total free amino acid concentration is reduced to the 2% sea water level within 12 hr. after transfer.
Free amino acid, haemolymph sodium and total body sodium levels after transfer to 2% sea water were compared.
The asymmetry between the fall in haemolymph sodium concentration and the decrease in total body sodium under these conditions is thought to be due to a water shift from the haemolymph into the tissues.
It is suggested that the osmotic pressure of the cells falls at a slower rate than that of the haemolymph.
