The zebraperch, Hermosilla azurea Jenkins and Evermann 1889, a warm-temperate member of the widespread but mainly tropical perciform family Kyphosidae, occurs in coastal waters of southern California and Baja California and in the Gulf of California (Jenkins and Evermann 1889; Miller and Lea 1972; Eschmeyer et al. 1983; de la Cruz-Aguero et al. 1994; Rodriguez-Romero et al. 1994; Thomson et al. 2000). The northerly range limit of this species was given as Monterey Bay (36Â° 36' N) by Miller and Lea (1972) and Eschmeyer et al. (1983), but the species has been regarded as uncommon in California (Miller and Lea 1972) and rare north of southern California (Eschmeyer et al. 1983). In the mid-1980s, zebraperch were captured in the Klamath River estuary in northern California (41Â° 31' N) to establish the northernmost range limit for the species (Fritzsche et al. 1991). In this note, we provide evidence that the northerly range extensions recorded for the zebraperch in recent decades correspond to short-term periods of ocean warming associated with El Nino conditions. We also offer support for the hypothesis that this fish has increased in abundance and established breeding populations in the Southern California Bight over the past 15-20 years coincident with a sustained warming trend in the region over the same time period.