A single triploid individual (3n = 75) of the California roach, Hesperoleucus symmetricus, was identified among a sample of nine specimens from the Russian River, California. The diploid number of H. symmetricus, as revealed by the karyotypes of the remaining eight specimens, is 50. Aside from the all-female triploid unisexual fishes, this is the first report of a triploid fish from the wild, and the second report of a triploid in a bisexual fish species. The most likely origin of the triploid was probably fusion of a haploid sperm with an unreduced ovum.