Silver carp (Hypophthalmichthys molitrix)

Synonyms: Leuciscus molitrix, Hypophthalmichthys dybowskii

Common Names: Invasive carp, Asian carp, flying carp, jumping carp, silver Asian carp

Description:

Silver carp (Hypophthalmichthys molitrix) is a large filter-feeding fish from eastern Asia, brought to the United States in the 1970s to clean algae from fish-farm and wastewater ponds [1]. It escaped into the Mississippi River system, spread through dozens of states, and is now pushing toward the Great Lakes, though it is not yet established there [1]. MISIN tracks it because it strips the water of the tiny plankton that native fish need, and because it leaps from the water when startled, injuring boaters [1][3].

Identification:

Silver carp is a big, deep-bodied, silvery fish that can grow over 3 feet long and weigh up to 60 pounds [1]. It is covered in very small silvery scales, with a scaleless head, and it fades from a greenish back to a silver-white belly [1]. Two features stand out: its eyes sit low on the head and point downward, below the level of its large, toothless, upturned mouth, and it has a sharp ridge (keel) running along the belly from the throat back to the tail [1]. Inside, its gills are lined with sponge-like filters it uses to strain plankton from the water [1].

The most memorable sign is its behavior: when startled by a boat motor, silver carp leap up to about 10 feet out of the water, often by the dozens, and can land in boats and injure people [3]. They are present year-round in the rivers they invade, and most active and visible in the warmer months [1].

At-a-glance cues:

1. Large, deep-bodied, silvery fish, often over 2 feet long [1]
2. Eyes set low on the head, pointing downward, below the mouth [1]
3. A sharp keel (ridge) along the belly from the throat to the tail [1]
4. Leaps high out of the water when startled by boat motors [3]

Habitat:

Silver carp lives in large rivers and their connected lakes, backwaters, and floodplains [1]. It is hardy, tolerating low oxygen and somewhat salty water, which helps it survive in a wide range of conditions [1]. As a filter feeder, its "hosts" are really its food ? it strains tiny floating plants and animals (plankton) from the water, the same food that native fish and young fish depend on [1].

The fish is native to eastern Asia, from the Amur River of far-eastern Russia south through much of China [1]. It is not native to North America. It is established in the Mississippi, Missouri, and Illinois river systems and is found in 30 or more states, but it is not established in the Great Lakes, where its arrival is a major concern [1].

Reproduction:

Silver carp would reach a new water body mostly through people moving it or its eggs. It spreads when live fish are stocked, dumped, or used as bait, and its tiny drifting eggs and young can be carried in water, livewells, and bait buckets [1]. Historically it escaped fish farms and wastewater ponds during floods and then spread on its own up connected rivers [1]. It is illegal under U.S. federal law to import silver carp or move it across state lines, because it is listed as injurious wildlife under the Lacey Act [1][2].

Once in a river, it breeds fast. Females release hundreds of thousands to millions of eggs in a season, and the eggs drift and hatch in flowing, turbid water [1]. In North America the fish can mature in as little as two years [1]. Because it is so productive and spreads by drifting young, stopping it depends on catching new populations early and keeping people from moving live fish or water between waterways [1].

Impact and Damage:

Silver carp is a direct hazard to people on the water. When a boat motor startles a school, the fish leap several feet into the air, and large, heavy fish landing in a moving boat have injured boaters, jet-ski riders, and water-skiers [3]. The fish is not poisonous, but the jumping makes infested waters dangerous for recreation [3].

For natural areas and fisheries, the bigger problem is what it eats. As a relentless filter feeder, silver carp strips plankton from the water ? the base of the food web ? competing with native filter feeders such as paddlefish, bigmouth buffalo, and gizzard shad, and with the young of nearly all fish species [1]. Studies in invaded rivers have documented declines in the body condition of native fish after silver carp moved in [1]. By removing this food, dense populations can reshape a river's entire food web, which is why its potential spread into the Great Lakes is treated as a serious threat [1].

Similar species:

Bighead carp (Hypophthalmichthys nobilis) is the closest look-alike ? another large invasive Asian carp with low-set eyes ? but it is dark gray with irregular blotches rather than uniform silver, and its belly keel runs only from the pelvic fins back, not all the way to the throat [1].

Grass carp (Ctenopharyngodon idella) is another invasive carp, but it has a torpedo shape, large scales, a forward-facing mouth, and no belly keel [1]. Common carp (Cyprinus carpio) is gold-brown with large scales and has two pairs of barbels (whiskers) at the mouth, which silver carp lacks [1]. Among natives, gizzard shad (Dorosoma cepedianum) is silvery and deep-bodied like a young silver carp, but it is much smaller, has a blunt snout with a small mouth, and a long trailing ray on its back fin [1].

Monitoring and rapid response:

Signs to watch for:

1. Large silvery, deep-bodied fish with low, downward-pointing eyes and a sharp belly keel [1]
2. Fish leaping out of the water ? sometimes many at once ? when a boat motor passes [3]
3. One caught by anglers anywhere it has not been confirmed before [1]

What you can do:

1. Never buy, keep, stock, transport, or release silver carp ? importing it or moving it across state lines is illegal under federal law [1][2].
2. Never dump bait buckets or move live fish between waters, and never release aquarium or pond fish into the wild.
3. If you catch one, do not put it back ? keep it, take clear photos, note the exact location, and report it right away (below) [1].
4. Clean, drain, and dry boats, livewells, and bait buckets when moving between waters so you do not carry eggs or young fish [1].
5. On waters where silver carp are present, slow down and stay alert, since the jumping fish can injure people [3].
6. For natural area crews and agencies, the priority is rapid response at the leading edge: confirm reports, and use targeted netting, commercial harvest, and barriers led by fisheries agencies to slow the spread, with eDNA and survey monitoring [1].

When to call a professional:

1. Any confirmed or suspected silver carp ? removing or responding to a large invasive fish is a job for your fisheries or natural resources agency.
2. Any water where one has been caught more than once, which may signal an establishing population.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Hypophthalmichthys molitrix (Silver Carp) ? Species Profile (summarizes Kolar et al. 2007, Sampson et al. 2009, Irons et al. 2007). nas.er.usgs.gov
2. U.S. Fish & Wildlife Service. Silver Carp (Hypophthalmichthys molitrix). fws.gov
3. Minnesota Department of Natural Resources. Silver Carp (Hypophthalmichthys molitrix). dnr.state.mn.us

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