Ecological Risk Screening Summary - Bitterling (Rhodeus sericeus) - 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.

Rhodeus sericeus (bitterling) is a small fish in the carp family, Cyprinidae. Its native range falls within the Amur River basin in western Asia (China, Mongolia, and Russia). Rhodeus species, possibly including R. sericeus, are in ornamental trade. A significant amount of taxonomic confusion has existed between R. sericeus and its close relative R. amarus. At present, these fish are considered two separate valid species, but have previously been considered subspecies of R. sericeus. The long history of modifications to their taxonomy results in confusion in the literature as to what information pertains to which species. This has complicated determining the identity of the Rhodeus species introduced in two rivers in New York. Based on current taxonomy and the current and historical treatment of the introductions in the literature this screening considers the New York introductions to be of R. amarus. Rhodeus sericeus is regulated in Hawaii, New Mexico, and Ohio. R. sericeus has been introduced to and established a population in the Tiber River in Italy. No information was found regarding impacts of this population. Regardless of taxonomic misunderstandings, both Rhodeus species parasitize mussels for reproduction, which creates a potential for negative impacts on mussel species outside of the bitterlings’ native range. However, no such impacts have been documented in Italy. History of invasiveness is therefore classified as Data Deficient. The climate match with the contiguous United States is high. Most of the contiguous United States had a high or medium climate match except the Atlantic, Gulf, and western areas. Some patches of medium match were found scattered in the Rocky Mountain areas. Certainty of assessment is low due to the history of taxonomic confusion and to lack of data for the history of invasiveness. The overall risk assessment category for Rhodeus sericeus is Uncertain.