Osmoregulation in Australian Freshwater Mussels (Lamellibranchiata). I. Water and Chloride Ion Exchange in Hyridella australis (Lam.)

Abstract

The chlorinities of the blood and pericardial fluid of H. australis are similar, but always exceed those of the normal external medium. A study of blood chloride changes in mussels in media of different concentrations has shown that immediately following a change of medium there is a change in blood chlorinity, which tends to assume a new equilibrium level within 24 hr. The rapidity with which this change occurs depends upon the difference between the chlorinity of the blood and that of the external medium. A study of water exchange under identical conditions has shown that significant changes occur in the hydration of the mussel. In hypotonic media the mussel can regulate its water content; in hypertonic media it cannot, but its hydration assumes a new level within 24 hr. It is concluded that some part of the body surface is permeable to both salts and water. The urine of the mussel is hypotonic to the blood; it remains remarkably stabre in chlorinity despite changes in blood chlorinity. The role of the kidney as a regulating organ is discussed. The significance of shell movements in osmoregulation is demonstrated. Shell closure has been shown to be an effective seal from the external medium, allowing the mussel to resist desiccation.