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

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Abstract
The emydid turtle C. borneoensis, nests on Malaysian ocean beaches with the true sea turtles. Adults were seen mainly in tidal upstream areas of the Perak and Setiu Rivers. Probably 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 wt loss of 0.9 and 1.4% body wt/day in 50 and 100% sea water (35.permill. salinity), respectively. In 25% sea water a net wt gain of 0.9% body wt/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 .cntdot. h, respectively. This is equivalent to a turnover of 16-18% of the body water daily (81% wt 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 .mu.mol/100 g .cntdot. h, which could be accounted for if a 50 g turtle drank only 10 .mu.l/h of the radioactive bath. Na efflux is even lower (.apprx. 1 .mu.mol/100 g .cntdot. h) and does not increase after injection of salt loads. Less than 0.5% of the total body Na content (82 .mu.mol/g) is lost daily. Hatchling C. borneoensis are not physiologically specialized for a life in estuaries of high salinity, yet they can survive for at least 2 wk in 100% sea water.

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