The Hippo pathway is an important regulator of organ size and tumorigenesis. It is unclear, however, how Hippo signaling provides the cellular building blocks required for rapid growth. Here, we report that transgenic zebrafish expressing an activated form of the Hippo pathway effector Yap1 develop enlarged livers and are prone to liver tumor formation. Transcriptomic profiling reveals that Yap1 reprograms genes involved in glutamine metabolism. Overall design: Analysis of gene expression in WT and lf:Yap transgenic zebrafish livers.