Calcium and phosphorus in unbanded eggs of the Nile crocodile (Crocodylus niloticus)

Abstract

Unbanded crocodilian eggs do not form an opaque band around their lesser circumference, indicating fertilization failure or early embryonic death. Assuming they represent fertile eggs prior to the onset of embryonic metabolism, the concentration and content of calcium (Ca) and phosphorus (P) in each component (shell, shell membrane, yolk and albumen) of unbanded farm-laid Nile crocodile (Crocodylus niloticus) eggs were described. The grouping effect of clutch (clutch effect) on each component's Ca and P concentration and content were assessed. Using regression models, the clutch size, clutch laying date, pond of origin, component mass and component Ca and P concentration were evaluated for an effect on each component's Ca and P content. Eggshell made by far the greatest contribution to total egg Ca whilst contributing no measurable P. Yolk contributed by far the greatest quantity of P and a significant quantity of Ca. Albumen contributed variable, but generally very low quantities of Ca and P to the egg. A strong clutch effect existed for shell Ca content and yolk Ca and P concentration and content. A very weak clutch effect existed for shell Ca concentration, and albumen Ca and P concentration. Shell membrane was an unreliable sample type in this study, likely reflecting issues with processing. Shell Ca and yolk Ca and P content were influenced primarily by component mass, and secondarily by element concentration. Albumen Ca and P content was principally influenced by element concentration. These descriptive findings will guide sample selection for future research.