Ion Composition and Osmolarity of Caspian Sea Ctenophore, Mnemiopsis leidyi, in Different Salinities

The aim was to study osmotic and ionic regulation in alien ctenophore, Mnemiopsis leidyi, acclimated gradually to different salinities (8, 13, 18 and 23 ppt) with the salt proportion of the Caspian Sea in laboratory conditions (24 ± 2 ˚C) on the samples with total length, 1. 5-3 cm. Results showed that this species is hyper-osmoconformer (maintaining internal osmolarity 2 – 22 mOsmol / l above external) in non lethal salinities ranging from 8 to 23 ppt. The results of ionic regulatory investigations revealed that this species can regulate calcium and sulphate ion so that the concentration of calcium ion in the internal fluid and sulphate ion in the external fluid were significantly more in 8 and 13 ppt, respectively. No regulation was observed about other ions such as Cl־, Mg2+ and K+ in the mentioned salinities.