Genotype for hypocretin receptor (hcrtr2) affects appetite in zebrafish

We investigated the role of hypocretin receptor in signaling appetite in zebrafish (Danio rerio). Hypocretin is a small neuropeptide known for its effects on circadian rhythm and appetite. Wild-type and heterozygous hu2098 (knockout for hcrtr2) zebrafish were raised to adulthood (3-4 months post fertilization) and genotyped. Feeding rate was measured directly using a novel technique that analyzed images of fish feeding continuously on brine shrimp, in which all individual brine shrimp were identified in a tank with a feeding fish. Fish were food restricted for 19-29 h before a feeding session, and feeding rate was determined by the regression of brine shrimp consumed/min over an eight-minute feeding period. Utilizing a mixed-effects ANCOVA model and accounting for mass as a covariate, heterozygous fish (hcrtr2⁺/hcrtr2^-) ate brine shrimp at a significantly faster rate (mean 23.4 ± 12.6 shrimp/min, n = 12) than wildtype fish (hcrtr2⁺/hcrtr2⁺) (20.5 ± 13.8 shrimp/min, p = 0.033, n = 11). These results support a role for hcrtr2 in appetite regulation.