EFFECT OF WATER RESTRICTION ON ENERGY AND WATER-BALANCE AND OSMOREGULATION OF THE FRUIT BAT ROUSETTUS-AEGYPTIACUS

The energy budget, water balance and osmoregulation of the fruit bat, Rousettus aegyptiacus, were studied during normal hydration and during water restriction (oven-dried apple diet). The water input and output were balanced during both normal hydration and water restriction. The kidney of the fruit bat is well adapted to handle the water load from its fruit diet by excreting large volumes (14% of the body mass per d ay) of dilute urine (113 +/- 25 mosmol . kg H2O-1) as well as reducing urine volume (- 95 %) and increasing urine osmotic concentration (555 +/- 280 mosmol . kg H2O-1) during water restriction. The haematocrit, plasma haemoglobin and total protein concentrations did not increase during water restriction and heat exposure, suggesting the conservatio n of plasma volume. Gross energy intake was not affected by water rest riction. However, digested energy intake and digestibility were signif icantly reduced. The effective regulation of energy and water budgets during water restriction suggests that the fruit bat can cope with sea sonal climatic changes and with variable fruit supply during various s easons.