Sperm-egg compatibility is essential to the evolutionary success of any sexually reproducing organism, yet the proteins that mediate gamete interactions often evolve at extraordinary rates. In threespine stickleback fish (Gasterosteus aculeatus) reproductive isolation is common in many recently derived populations throughout the Northern Hemisphere, but the precise biochemical mechanisms driving this isolation are unknown. Stickleback are classic models of molecular adaptation and speciation, and while rapidly evolving reproductive proteins are probable candidates underlying reproductive isolation they remain unexplored in this model evolutionary system. Tandem mass spectrometry was used to characterize the secreted proteomes of stickleback eggs from Lake Union, Washington. High-resolution mass spectra were acquired, with homologs of common vertebrate egg proteins identified. Evolutionary rate analysis (dN/ds) of these homologs across fish from superorders within the Teleosts indicates positive selection. In contrast to mammals, the genes encoding the major egg proteins are tandemly duplicated in the stickleback genome. Such duplications provide a substrate for diversification that can drive rapid evolution, and suggest a potential mechanism underlying sexual conflict within stickleback populations and ultimately speciation.