Indian Journal of Geo-Marine Sciences Vol. 41(5), October 2012, pp. 468-472 Oxygen consumption rate of the estuarine Psammobiid clam Soletellina diphos (linnaeus) under various Environmental conditions S. S. Taware *, V. M. Lagade & D. V. Muley Department of Zoology, Shivaji University Kolhapur – 416 004, India * [E-mail: tawareshital_21@rediffmail.com], Received 15 April 2011; revised 17 August 2011 Oxygen consumption rate (OCR) of the estuarine clam, Soletellina diphos (Linnaeus) was studied in the laboratory. The OCR was measured against a range of body size and weight, and under conditions of starvation, aerial exposure, temperature and low salinity. The pattern of diurnal rhythm was also investigated. The OCR was found to be inversely related to body size and body weight. It decreased considerably with starvation but, with exposure to atmospheric air, it increased up to 3rd hour and reached to the normal level by the 5th hour. The OCR increased with rise in temperature from 20 oC to 35 oC. It altered with decrease in salinity as compared to normal salinity (38 ‰), it was highest at 70 % and lowest at 40 % of normal seawater. A distinct diurnal rhythm in OCR was observed in these clams. The OCR was greater around afternoon and at a lowest level around midnight. [Keywords: Soletellina diphos, oxygen consumption rate (OCR), environmental conditions.] Introduction Bivalves are burrowing, filter feeding, and gill- breathing as well as mantle-breathing organisms. Exchange of gas occurs at gill or mantle and finally water exits through exhalant siphon 1 . Changes in environmental conditions affect the metabolic rate of such organism 2, 3 . During low tide, the intertidal zone of an estuary gets exposed to atmospheric air and the external surface of clams such as Soletellina diphos that are buried in mud remain uncovered with water for certain period. Under such condition, the physiological and metabolic processes of clams differ from those operating during tidal conditions. Water temperature is a major environmental factor controlling the distribution range of marine and estuarine organisms, and strongly influencing their physiological processes. The positive relationship between water temperature and metabolic rates has been well documented in many groups 4, 5, 6 . Estuarine animals have better ability to acclimatize to variations in salinity during low and high tide; under these circumstances the estuarine animals have better adaptability to the changing environment than do those from more stable marine habitat. Salinity is a major environmental factor for controlling the physiological processes of estuarine organisms, such as, feeding, growth, respiration and reproduction 7, 1 . Many studies on marine bivalves have been carried out using species such as Martesia striata 8 , Meretrix meretrix 9 , Katelysia opima 10 and Paphia laterisulca 11 . The metabolism and the growth rate of the hard clam, Mercenaria mercenaria, were investigated in a population inhabiting Southampton Water in southern England 12 . Present study consists clam species, S. diphos from Bhatye estuary near Ratnagiri, west coast of Maharashtra. The present investigation was undertaken to study the metabolic rate by measuring oxygen consumption rate (OCR) of S. diphos in relation to the various environmental factors like body size, body weight, temperature, salinity, air exposure, starvation and diurnal rhythm. Materials and Methods Animal collection and maintenance The estuarine clam, S. diphos was collected from Bhatye estuary (16 o 51’ N, 73 o 15’ E) near Ratnagiri during low tide. The clams were cleaned and washed with the sea water and were acclimatized for 48 hours in laboratory conditions. Experimental set The OCR was determined using special apparatus developed in the laboratory resembling the Galtsoff and Whipple apparatus 13 . OCR was estimated by using glass respiratory jars having 1 lit. capacity. Jars were wrapped with black papers to provide natural habitat to each individual clam. The selected clams of