GROWTH, WATER, AND ENERGY-METABOLISM OF THE SOFT-SHELLED TURTLE (TRIONYX-TRIUNGUIS) EMBRYO - EFFECTS OF TEMPERATURE

The Nile soft-shelled turtle (Trionyx triunguis) lays about 40 18-g hard-shelled eggs in a nest cavity buried 20-40 cm deep in sand banks along rivers. The eggs exchange heat, water, and gases with the surrounding substrate during the 65-75-d incubation. Measurements to determine the effect of constant incubation temperature (T(i)) on embryonic growth and egg O2 consumption (Vo2) were conducted in the laboratory. Energy and water balances for the egg and embryo were constructed. Hatching success increases above 24-degrees-C and declines above 33-degrees-C. Embryonic growth exhibited a sigmoid pattern and was significantly affected by T(i). Egg Vo2 increased during the first half of incubation, peaking at about 82% of incubation, and then decreased by about 30% during the remaining incubation time. Peak Vo2 was significantly affected by T(i), but the final Vo2 just prior to pipping and hatching was not. Peak Vo2 was about 50-70 mL . d-1 at standard temperature and pressure for dry gas (STPD), and final Vo2 was around 34-37 mL (STPD) . d-1. The total O2 consumption (1,283 mL . egg-1) was not affected by T(i). The O2 cost of incubation was 72 mL (STPD) . g-1 fresh egg and 108 mL (STPD) . g-1 yolk-free batchling. Within the range of T(i) tested, no significant differences were observed in yolk-free batchling wet mass (11.8 g), water fraction (78%), or energy content and density (24 kJ . g-1 dry mass). Nor were differences observed in residual yolk wet mass (0.4 g), its water fraction (51%), or its energy content and density (31 kJ . g-1 dry mass). Approximately 21% of the water present in the egg is available for loss to the environment. The 21% of the water present in the egg is available for loss to the environment. The energy balance indicated that the gross production efficiency was around 70%, while total production efficiency was around 68%. The energy lost from metabolic inefficiency was around 28.4% of the total energy utilized during incubation. The patterns of growth, O2 consumption rate, and allocation of energy of T. triunguis eggs and embryos were similar to those reported for avian species.