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

Abstract

The effects of oxygen partial pressure (\( P_{{{\text{O}}_{2} }} \)) 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 \( P_{{{\text{O}}_{2} }} \), 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 (\( G_{{{\text{O}}_{2} }} \)) in gas exchange was also examined under selected environmental \( P_{{{\text{O}}_{2} }} \) and temperatures. The breakdown of the vitelline membrane changed capsule geometry, allowed water to be absorbed into the perivitelline space and increased capsule \( G_{{{\text{O}}_{2} }} \). This occurred at embryonic stage 32 under all treatments and was largely independent of both \( P_{{{\text{O}}_{2} }} \) and temperature (15, 20 and 25°C), demonstrating that capsule \( G_{{{\text{O}}_{2} }} \) cannot adaptively respond to altered environmental conditions. The membrane breakdown increased capsule diffusive \( G_{{{\text{O}}_{2} }} \) and stabilised perivitelline \( P_{{{\text{O}}_{2} }} \), but reduced the convective \( G_{{{\text{O}}_{2} }} \) of the perivitelline fluid, as the large perivitelline volume and inadequate convective current resulted in a \( P_{{{\text{O}}_{2} }} \) gradient within the egg prior to hatch.