The sponge species Sigmadocia carnosa (Dendy, 1889) and Mycale mytilorum (Annandale, 1911) belong to the class demospongiae were collected from the Vizhinjam port of South India and examined for ouabain sensitive Na+, K+-ATPase specific activity in tissue homogenates. The total protein contents including stress proteins in the tissues were measured with the help of a modified Biuret assay. A species specific activity of Na+, K+-ATPase was found in the tested marine sponges. A time dependent significant increase in Na+, K+-ATPase activity was found in Sigmadocia carnosa at diluted sea water. The Na+, K+-ATPase activity in Mycale mytilorum also showed significant rise particularly during 1 and 4 hour at diluted sea water exposure. The total protein contents in both species showed no significant change during exposure to dilute sea water.
Key words: Sigmadocia carnosa, Mycale mytilorum, Na+-K+-ATPase activity, Osmotic challenge, protein content.