The global obesity epidemic demands an improved understanding of the developmental and environmental factors regulating fat storage. Adipocytes serve as major sites of fat storage and as regulators of energy balance and inflammation. The optical transparency of developing zebrafish provides new opportunities to investigate mechanisms governing adipocyte biology, however zebrafish adipocytes remain uncharacterized. We have developed methods for visualizing zebrafish adipocytes in vivo by labeling neutral lipid droplets with Nile Red. Our results establish that neutral lipid droplets first accumulate in visceral adipocytes during larval stages and increase in number and distribution as zebrafish grow. We show that the cellular anatomy of zebrafish adipocytes is similar to mammalian white adipocytes and identify peroxisome-proliferator activated receptor γ and fatty acid binding protein 11a as markers of the zebrafish adipocyte lineage. By monitoring adipocyte development prior to neutral lipid deposition, we find that the first visceral preadipocytes appear in association with the pancreas shortly after initiation of exogenous nutrition. Zebrafish reared in the absence of food fail to form visceral preadipocytes, indicating that exogenous nutrition is required for adipocyte development. These results reveal homologies between zebrafish and mammalian adipocytes and establish the zebrafish as a new model for adipocyte research
