Ecological Risk Screening Summary - Dusky Millions Fish (Phalloceros caudimaculatus) - Uncertain Risk

Species that are considered uncertain risk need a more in-depth assessment beyond the Risk Summary to better define the species’ risk to U.S. environments.

Phalloceros caudimaculatus, Dusky Millions Fish, is a small, stout fish species native to Brazil, Argentina, and Uruguay. Possessing a high tolerance to a wide range of water temperatures, P. caudimaculatus can thrive in a wide range of habitats where it primarily feeds on detritus and algae. Introductions have been reported in Malawi, Australia, and New Zealand, and established populations are confirmed for Malawi and Australia. Some introductions could have been intentional attempts to control mosquito populations. P. caudimaculatus used to be popular in the aquarium trade in Australia but is now rare. No impacts of P. caudimaculatus on native species have been documented, although there is concern over competition and predation on native fishes. P. caudimaculatus has been documented to displace previously established nonnative populations of a closely-related species, Gambusia holbrooki. History of invasiveness is classified as “None Documented.” No introductions of P. caudimaculatus have been reported within the contiguous United States. However, the overall climate match is high, with most of the southern contiguous United States having high or medium match. Certainty of assessment is low because of the lack of information on impacts of introduction. The overall risk assessment category for P. caudimaculatus is “Uncertain.”