The spontaneous mutant blond of the guppy, Poecilia reticulata, was mapped using ddRADseq in combination with QTL mapping. We used a mapping cross comprised of 134 F2 individuals to identify a candidate region for blond, which contained three candidate genes. All blond fish were homozygous for a 2-bp deletion in adenylate cyclase 5 (adcy5), which is predicted to cause a splicing defect of intron 1 and a premature stop codon. Blond therefore corresponds to the guppy orthologue of adcy5.