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.

Crucian carp (Carassius carassius) is native to the northern areas of Europe and Asia. It has been used throughout history as a food fish and continues to be used as a food source and sport fish. Crucian carp are hosts of pathogens that cause three OIE-reportable diseases. C. carassius is physically similar to several other species, and can hybridize with those species, which may lead to identification problems. The history of invasiveness has not been documented. Records of introduction were found resulting in established populations. C. carassius is reported to possibly impact native fish species and cause other community changes through increasing turbidity through its feeding behaviors but there is no peer-reviewed support of these impacts. C. carassius was introduced in Chicago in the early 1900s but this population has been extirpated. The climate match is high. Most of the contiguous United States had a medium or high match. Areas of low match were found only inland along the Gulf Coast, southern Arizona, and along the northern Pacific Coast. The certainty of assessment is medium. The cryptic nature of the species and lack of impact information reduces the confidence. The overall risk assessment category is uncertain.