We used microarray analyses in adult female zebrafish (Danio rerio) to identify metabolic pathways regulated by starvation in two key organs that 1) serve biosynthetic and energy mobilizing functions (liver) and 2) consume energy and direct behavioral responses (brain). Starvation affected the expression of 574 transcripts in the liver, indicating an overall decrease in metabolic activity, reduced lipid metabolism, protein biosynthesis and proteolysis, and cellular respiration, and increased gluconeogenesis. Starvation also regulated expression of many components of the Unfolded Protein Response, the first such report in a species other than yeast (Saccharomyces cerevisiae) and mice (Mus musculus). The response of the zebrafish hepatic transcriptome to starvation was strikingly similar to that of rainbow trout (Oncorhynchus mykiss), but very different from common carp (Cyprinus carpio) and mouse. The transcriptome of zebrafish whole brain was much less affected than the liver, with only two differentially expressed genes, both down-regulated. Down-regulation of one of these genes, matrix metalloproteinase 9 (mmp9), suggests increased inhibition of apoptosis (neuroprotection) and decreased restructuring of the extracellular matrix in the brain of starved zebrafish. The low level of response in the transcriptome of whole zebrafish brain agrees with observations that the brain is metabolically protected compared to the rest of the body.