News / Species Spotlight / Guam Chromis (Pomachromis guamensis) (02/28/18)

Guam Chromis (Pomachromis guamensis)

Species Spotlight - Guam Chromis (Pomachromis guamensis)
The Pomachromis damselfishes are a small and little-known group found across the Indo-Pacific. Four species are currently recognized, though this number is likely underrepresenting their true biodiversity given how geographically widespread they are. Of these, the most restricted in distribution is a species known only from the Mariana Arc, the Guam Chromis (Pomachromis guamensis).

All of these species typically occur in a similar ecological niche, favoring shallow surge-swept forereefs exposed to the open ocean, though there are also reports from greater depths and, at least in Micronesia, from flat topped mid-lagoon pinnacles. Sometimes these habitats are loaded with branching Acropora and Pocillopora, and at other times they occur in rocky reefs completely devoid of corals. The common element here is an open habitat prone to swift currents, which bring a steady supply of the small zooplankton upon which these damselfishes feed.

Species theyve been spotted with in the wild include the Micronesian Damselfish (Pomacentrus micronesicus), the Midget Chromis (Chromis acares), the Scaly Damselfish (Pomacentrus lepidogenys), the Bicolor Chromis (Chromis margaritifer), and the Blueside Fairy Wrasse (Cirrhilabrus cyanopleura). Combining these in a suitably large aquarium should be very doable given the relatively mild manners of all these species and would result in a unique and visually stunning biotope.

Among the Pomachromis, the endemic species from Guam and the Mariana Islands stands out for its lack of black in the caudal fins, whereas in other species a pair of black stripes line the lobes of the caudal fin. Mature specimens have a somewhat dingy appearance to their otherwise silver bodies, with darker margins along the scales, all accented by a bright yellow caudal and dorsal fin which can bleed into the top of the head slightly. All Pomachromis are rather uncommon within the aquarium trade, but this is especially so for P. guamensis given the limited collection that takes place within its small geographic distribution, but this is certainly one group in need of more appreciation.