Effects of environmental oxygen on development and respiration of Australian lungfish (Neoceratodus forsteri) embryos

The effects of oxygen partial pressure (PO₂) on development and respiration were investigated in the eggs of the Australian lungfish, Neoceratodus forsteri. At 20°C, embryonic survival and development was optimal at 15 and 20. 9 kPa. Development was slowed at 5 and 10 kPa and embryos did not survive 2 kPa. At lower PO₂, the rate of oxygen consumption also decreased. Embryos responded to hypoxia by hatching at an earlier age and stage of development, and hatching wet and dry gut-free masses were reduced. The role of oxygen conductance (GO₂) in gas exchange was also examined under selected environmental PO₂ and temperatures. The breakdown of the vitelline membrane changed capsule geometry, allowed water to be absorbed into the perivitelline space and increased capsule GO₂. This occurred at embryonic stage 32 under all treatments and was largely independent of both PO₂ and temperature (15, 20 and 25°C), demonstrating that capsule GO₂ cannot adaptively respond to altered environmental conditions. The membrane breakdown increased capsule diffusive GO₂ and stabilised perivitelline PO₂, but reduced the convective GO₂ of the perivitelline fluid, as the large perivitelline volume and inadequate convective current resulted in a PO₂ gradient within the egg prior to hatch.12 page(s