According to a recently published developmental study of lipid composition performed by liquid chromatography-mass spectrometry (LC-MS), at the time of fertilization, embryo lipids are approximately 40% cholesterol, 35% PL, and 9% TG, with less abundant species, including mono- and di-glycerides, cholesterol esters (CE), ceramides, and lysophospholipids, making up the remainder (24). Over the first 5 days of life, a linear decrease in the molar amount of most lipid species is observed in the yolk with a corresponding increase in the embryonic/larval body. Some exceptions have been observed: TG in the body remains consistently low as it is depleted from the yolk, suggesting that yolk TGs are primarily broken down and either oxidized for energy or resynthesized into other lipid products. Interestingly, CE, the other “energy storage” lipid class, is exchanged evenly from the yolk to the body during this period of development with the total amount remaining the same (24). Cholesterol synthesis in animal cells is tightly controlled in response to the cholesterol content of membranes via regulation of HMG-CoA reductase expression, and esterification is a major mechanism by which excess cholesterol is neutralized (25). One possible reason that CE is not depleted during the lecithotrophic (yolk-feeding) period of development is that breaking down CE for fatty acid oxidation would result in an overabundance of cholesterol. Favoring glycerolipids as an early energy source, therefore, would be important for cholesterol homeostasis, while CE from the yolk could be repackaged into intracellular lipid droplets for later oxidation or storage in adipocytes. Free cholesterol in the yolk and the body decrease and increase, respectively, at the same apparent rate between 24 h and 5 days of development, but the cholesterol content of the body at 5 dpf is less than the initial amount in the yolk (24). It is likely that this portion of the cholesterol is directed to synthesis of steroid hormones and bile, though these compounds were not measured in this study.