OBJECTIVETo establish a diet-induced obesity model in zebrafish larvae.

METHODSAt 7 days post-fertilization (dpf), 200 zebrafish larvae with normal development were randomly allocated to two groups with the feeding quantity of 30 mg per day (normal feeding group) or 180 mg per day (overfed group) for 20 days. The weight, length, BMI, triglyceride (TG) and total cholesterol (TCH) of each group were measured. Whole-mount Oil Red O staining, frozen Oil Red O staining and hematoxylin-eosin (HE) staining were used to estimate the rate of hepatic steatosis and liver histology of the zebrafish. The dynamic change of hepatic lipid droplets and distribution of adipose tissue were observed with Nile Red staining in overfed zebrafish in vivo.

RESULTSThe weight, length, BMI and TG of overfed zebrafish were significantly increased compared with those in normal feeding group. Whole-mount Oil Red O staining showed that the percent of hepatic steatosis in overfed group (89.4%) was markedly higher than that in normal feeding group (20.7%). Macrovesicular steatosis was observed in the liver of the overfed larvae. Nile Red staining visualized hepatic lipid droplets and the distribution of larval adipose tissue, which increased with feeding time in the overfed zebrafish. Starving larvae showed depletion of fat and hepatic lipid, and adipose tissue was induced after refeeding.

CONCLUSIONSWe successfully established an diet-induced obesity model in zebrafish larva, in which Nile Red staining allows in vivo observation of the adipocytes and hepatic lipid droplets.