Asian carp refer to four species of freshwater fish: Bighead, Silver, Grass, and Black carp. These species are considered invasive in North America, having been introduced from their native Eurasia in the 1970s, primarily for aquaculture purposes. Their presence poses a concern for the health of aquatic ecosystems, as they can outcompete native fish for food and disrupt natural food webs. Recognizing the signs of their presence is a step toward managing their spread and protecting local aquatic environments.
Visual Identification of Asian Carp Species
Identifying Asian carp involves recognizing their distinct physical characteristics. Bighead carp (Hypophthalmichthys nobilis) have a large, scaleless head and mouth, with a protruding lower jaw without teeth. They have a dark gray coloration on their backs that fades to white on their bellies, often with dark blotches on their sides. These deep-bodied fish can grow to over 80 pounds and reach lengths of up to 5 feet.
Silver carp (Hypophthalmichthys molitrix) are smaller than Bighead carp, weighing around 20 to 80 pounds. They have an upturned lower jaw and eyes positioned low on their broad head, below the body’s axis. Their bodies are silver with a slate gray head and dorsal surface, and a keel extending from the anal fin to the throat.
Grass carp (Ctenopharyngodon idella) weigh around 65 pounds and can reach over 80 pounds and lengths exceeding 5 feet. They have an oblong body and a flattened head. Their large, overlapping scales often have dark edges, creating a cross-hatched appearance.
Black carp (Mylopharyngodon piceus) are elongated and laterally compressed with a pointed head. Their coloration ranges from brown to black on the back, fading to a gold sheen or bluish-grey on the belly. These fish have large, pavement-like teeth in their throat, which crush mollusk shells, their primary food source. Black carp can grow to over 5 feet long and weigh up to 150 pounds.
Behavioral Clues
Observing specific behaviors can indicate the presence of Asian carp, even when direct visual identification is challenging. Silver carp are known for their jumping behavior. When startled by disturbances like boat motors, these fish can leap out of the water, sometimes as high as 10 feet. This response is triggered by the sound or turbulence created by passing watercraft.
Bighead and Silver carp exhibit schooling patterns, traveling in large numbers. Their continuous feeding habits, due to their lack of a true stomach, cause surface activity as they filter large amounts of plankton. Grass carp primarily consume aquatic vegetation, and their foraging can cause surface disturbances, especially in areas with dense plant growth. Black carp, which feed on snails and mussels, cause less obvious surface disturbances, but their presence can be inferred by impacts on mollusk populations.
Environmental Indicators
Changes in the aquatic environment serve as indirect signals of Asian carp presence. Bighead and Silver carp are filter feeders that consume large quantities of plankton. Their feeding activity increases water turbidity or muddiness as they stir up bottom sediments, reducing water clarity. This cloudiness hinders native fish from finding food and covering their eggs, impacting their survival.
Grass carp, by contrast, primarily consume aquatic vegetation, and their feeding habits alter plant communities. They can uproot plants and disturb lake and river bottoms, leading to a reduction in aquatic plants that provide habitat, shelter, and spawning grounds for native fish. A decline in native fish populations, especially those that compete for plankton or rely on aquatic vegetation, can be a symptom of Asian carp outcompeting them for food resources.
Reporting Suspected Sightings
If you suspect you have identified an Asian carp, reporting the sighting is an important step for monitoring and management. Do not return the fish to the water if caught. Document the sighting by taking clear photos of the fish, noting the exact location, and recording the date.
The U.S. Geological Survey’s Nonindigenous Aquatic Species Program (NAS) provides an online platform for reporting sightings nationwide. Alternatively, contact your state government’s natural resource agency or local wildlife agencies directly. Public reports contribute to understanding the distribution of invasive species, aiding researchers in predicting susceptible regions and developing control strategies.