Although Fraher and colleagues’ published analysis of their LC-MS data set was limited to discussion of developmental changes in lipid classes, quantitation of all individual lipid species was published as a supplement to the manuscript. These data provide an opportunity to examine the changes in individual lipid species that occur during the first 5 days of zebrafish development. For example, the major PL classes are defined by head group (e.g., PCs, phosphatidylethanolamines, phosphatidylserines, etc.), but each of these classes comprises thousands of different molecules with different types of fatty acid “tails.” Modern mass spectrometry technologies optimized for lipidomics can differentiate between individual lipid species at this level of resolution because they can precisely determine the mass to charge ratio (m/z) of each analyte in a mixture and because they employ a second step in which the molecules are fragmented and the subsequent m/z values of these fragments are also determined. Complex lipids such as PLs are identified using m/z values calculated from molecular formulas and expected fragmentation patterns, and are annotated in Fraher’s supplemental data and other lipidomics data sets as “Head Group (FA 1/FA 2).” The most abundant PL in animal cell membranes, for example, is PC with the saturated 16-carbon fatty acid palmitate and the monounsaturated 18-carbon fatty acid oleate and is annotated as PC(16:0/18:1). When the specific fatty acid composition of a complex lipid cannot be determined, only the total fatty acid carbon chain length and number of unsaturated carbon–carbon bonds is given [e.g., PC(34:1)].