HYPOXIA INDUCES SURFACING BEHAVIOR IN BROWN-STRIPED FROG (LIMNODYNASTES PERONII) LARVAE

In their natural habitat, brown-striped frog (Limnodynastes peronii) l arvae periodically swim rapidly from the bottom of their ponds to the water surface and then immediately dive to the bottom again. This beha viour is presumably related to air-breathing. We examined the behaviou ral and metabolic responses to aquatic hypoxia in L. pernoii larvae. G as filled lungs were found in all free-swimming larval stages of L. pe ronii, but air-breathing occurred infrequently in normoxic water. The frequency of air-breathing at 30 degrees C increased rapidly in hypoxi c water when oxygen partial pressure (P-O2) fell below 10 kPa. Only a slight increase was observed at similar oxygen partial pressures at 20 degrees C. The critical oxygen tension at 30 degrees C was about 7 kP a, below which, aquatic breathing larvae become metabolic oxygen confo rmers. In natural habitats where surfacing behaviour was observed, tem peratures during summer months frequently exceed 25 degrees C and some ponds become extremely hypoxic (P-O2 < 3.0 kPa); therefore air-breath ing appears to be the only way in which these larvae can maintain a fu lly aerobic metabolism.