Yamato Tachibana (Tachibana; Citrus tachibana) is an endemic fruit and represents one of the oldest citrus species in Japan; it is grown in the Mie Prefecture. It has been attracting attention for its cultural heritage and unique scent. To evaluate biological activities of Tachibana, we fed several parts of the Tachibana fruit (whole fruit, pulp [albedo and segment wall], and flavedo) to adult zebrafish and found that Tachibana increased body weight and plasma triglycerides besides increasing overall food intake. We then created a simple fluorescence-based feeding assay using dried rotifer sheets and larval zebrafish (6 days postfertilization) to screen the various extracts of Tachibana parts. We found that water extracts of Tachibana pulp increased feeding volume in zebrafish. Although citrus species are believed to prevent obesity and obesity-associated diseases in general, our findings showed that water extracts of Tachibana increase food intake in zebrafish and lead to an increase in body weight. We suggest that Tachibana might reverse appetite loss in lean populations and may prove beneficial in aiding fish cultivation.