Composition and energy density of eggs from two species of freshwater turtle with twofold ranges in egg size

Abstract

Lipid, protein, ash, carbohydrate and water content and energy density of eggs were measured from different clutches over a range of egg size in two species of freshwater turtle. Dry egg contents consisted of protein (54–60%), lipid (25–31%) and ash (5–6%) while carbohydrate was found to be negligible (<1%). Albumen consisted principally of water (∼98%), and the dry component was composed of protein (47–51%), ash (19–26%) and lipid (18–21%), but contributed only a small amount (∼2%) to overall dry egg contents. Energy density of dry albumen (15–17 kJ/g) was significantly lower than for dry yolk (26–27 kJ/g). Yolk consisted of 62–70% water, and the dry component was composed of protein (54–61%), lipid (25–31%) and ash (5–6%). Fractional concentrations of water, lipid, protein and ash and energy density remained constant over the range of egg size in Emydura signata eggs. In contrast, an increase in the yolk to albumen ratio and a decrease in water content of yolk as egg size increased caused the composition and energy density of Chelodina expansa eggs to vary systematically with egg size.