Osmoregulation in Sea Water of Hatchling Emydid Turtles, Callagur borneoensis, from a Malaysian Sea Beach

Abstract

The emydid turtle Callagur boreoensis nests on Malaysian ocean beaches with the true sea turtles. Adults were seen mainly in tidal upstream areas of the Perak and Setiu Rivers. It is likely that hatchlings must swim through the sea to reach the river mouths, yet they are intolerant of long term immersion in sea water when tested in the laboratory. Fasting turtles in the initial week of exposure undergo a net weight loss of 0.9 and 1.4% body weight/day in 50% and 100% sea water (35%o salinity) respectively. In 25% sea water a net weight gain of 0.9% body weight/day was recorded. Turtles move to or remain in fresh water when given a choice between it and sea water in a divided tank. In 100% sea water, body water influx and efflux were 0.616 and 0.546 ml/100 g-h, respectively. This is equivalent to a turnover of 16-18% of the body water daily (81% weight is water). Influx must be mainly occurring through the skin and/or shell since turtles apparently do not drink 100% sea water. This is proven by the very low Na influx, 5.6 /umoles/ 100g.h, which could be accounted for if a 50g turtle drank only 10 /l/h of the radioactive bath. Na efflux is even lower (about 1 /mole/100g-h) and does not increase after injection of salt loads. Less than 0.5% of the total body Na content (82 /moles/g) is lost daily. Hatchling C. boreoensis are not physiologically specialized for a life in estuaries of high salinity, yet they can survive for at least two weeks in 100% sea water.