Aromatase (Cyp19a1) is the steroidogenic enzyme that converts androgens into bioactive estrogens, and hence is in a pivotal position to mediate reproduction and sexual behavior. In teleosts, there are two aromatase paralogs:cyp19a1athat is highly expressed in granulosa and Leydig cells in the gonads with critical function in sexual differentiation of the ovary, andcyp19a1bthat is highly expressed in radial glial cells in the brain with unknown roles in reproduction.Cyp19a1-/-mutant zebrafish lines were used to investigate the importance of thecyp19a1paralogs for spawning behavior and offspring survival and early development. Mutation ofcyp19a1bwas found to increase the latency to the first oviposition in females. Mutation ofcyp19a1bin females also increased the number of eggs spawned; however, significantly more progeny died during early development resulting in no net increase in female fecundity. This finding suggests a higher metabolic cost of reproduction incyp19a1b-/-mutant females. In males, the combined mutation of bothcyp19a1paralogs resulted in significantly lower progeny survival rates, indicating a critical function ofcyp19a1during early larval development. These data establish the specific importance ofcyp19a1bfor female spawning behavior and the importance of thecyp19a1paralogs for early larval survival.