The initial amount of lipid contained in the egg varies between species, and species with lengthier incubation times tend to have higher initial percent lipid content (Kaitaranta and Ackman, 1981). Eggs that contain oil globules also have high percent lipid content (Eldridge et al., 1983; Jobling et al., 1995; Tocher, 2003), and while oil globules may aid buoyancy
in some species, the high lipid content indicates an important role for nutrition.