Carps

In Arkansas, carps are an invasive (exotic or non-native) species whose introduction has caused economic and/or environmental damage. To date, there are five species of invasive carps that have entered or have been deliberately introduced into Arkansas for various reasons, and all belong to the order Cypriniformes and the minnow family Cyprinidae. Many of these fish originated from Asia or Europe, were introduced into North America, and pose a major threat to the ecology of native fishes, the environment, and the economy of fisheries in Arkansas. The longer it takes to respond to the damage done to an ecosystem done by these fish, the more money and time must be spent restoring and protecting that ecosystem.

Grass Carp
The grass carp or white amur, Ctenopharyngodon idella, is one of the largest members of the minnow family and is one of the four Asian carp species present in the state. It is a sub-tropical to temperate species, native to large lakes and rivers in eastern Asia extending from the Amur River in Russia and China, southward to northern Vietnam, and from coastal waters inland.

In the United States, they were originally imported in 1963 from eastern Asia by the Bureau of Sports Fisheries and Wildlife (which later became the U.S. Fish and Wildlife Service) on an experimental basis to assess their potential to control submersed aquatic vegetation (particularly Hydrilla) in aquaculture ponds. The two sites where they were used were Auburn, Alabama, and the Fish Farming Experimental Station in Stuttgart (Arkansas County). The Arkansas stock was imported from Malaysia, while the Auburn stock came from Taiwan. In the mid-1960s, the Arkansas Game and Fish Commission (AGFC) started to raise C. idella at the state fishery hatchery in Lonoke (Lonoke County). Unfortunately, many of the early stockings in Arkansas were in lakes or reservoirs open to stream systems. In addition, C. idella orient themselves to flow and will quickly leave ponds when water is flowing over a spillway, and as a result, many escaped from these aquaculture facilities soon after importation. Specimens in the wild were first documented along the Illinois portion of the Mississippi River in 1971. In the early 1970s, grass carp began to appear in the catches of Arkansas’s commercial fisheries, and by 1976, twenty-five tons were reported taken statewide. Thousands of grass carp are reared and sold by fish farmers in Missouri and Arkansas.

By 2020, C. idella had quickly spread to forty-five states (every state but Alaska, Maine, Montana, Rhode Island, and Vermont) through the accidental and intentional, legal and illegal, release by numerous state and federal agencies, private groups, and individuals for control of aquatic vegetation in culture ponds. Breeding populations have been reported along major rivers, including the Mississippi, Illinois, and the Trinity River (Galveston Bay area) in Texas. In Arkansas, grass carp are scattered across the state at sites ranging from manmade impoundments to large rivers.

Grass carp are prodigious feeders (capable of consuming up to three times of their body weight per day in plant material), as well as being explosive breeders. Unlike other carps, C. idella prefer to spawn in large rivers instead of lakes or slower-moving waters. This negative biological factor is potentially dangerous, as larger rivers flow through many states, which could further their invasion.

Seven of the main negative biological impacts on native species by C. idella are reported to include: (1) competition for food with invertebrates (especially crayfish) and other fishes, (2) significant changes in the composition of aquatic vegetation, phytoplankton, and invertebrate communities, (3) interference with the reproductive biology of other fishes, (4) modification or elimination of preferred fish habitats, (5) enrichment and eutrophication of lakes, (6) disruption of food webs and trophic structure, and (7) introduction of non-native diseases and parasites that local species may not have a resistance to, which may lead to local extinction events and lasting changes in ecosystem dynamics. For example, it is generally thought that grass carp imported from China were the source of introduction of the Asian fish tapeworm, Schizocotyle acheilognathi. However, the long-term effects of introduced grass carp on an aquatic site are complex and apparently depend on the stocking rate, macrophyte abundance, and community structure of the ecosystem.

The stout body of the grass carp is elongate with moderately large scales, a blunt head without scales or barbels, and a terminal mouth. There are eight (or, rarely, nine) dorsal fin soft rays, thirty-seven to forty-seven lateral line scales, six or seven scale rows above the lateral line, nine (or, rarely, eight or ten) anal fin soft rays, and fifteen to twenty pectoral fin soft rays. Grass carp are silvery pale gray to olive in color, with scales of dorsum and sides having prominent dark edges, producing a cross-hatched pattern. Grass carp differ from goldfish (Carassius auratus) and Common Carp (Cyprinus carpio) in having a shorter dorsal fin (only seven to eight rays) and from both Hypophthalmichthys species (bighead and silver carps) in having fewer anal rays (9 or fewer) and fewer but larger lateral scales. This species typically reaches sizes of 27 to 36 kg (65 to 80 lbs.) in its native habitat, but a few larger individuals have been caught with lengths up to 125 cm (49.2 in.). The all-tackle world record for C. idella was a specimen caught in Bulgaria in 2009 that weighed 39.8 kg (87 lbs., 10 oz.). In Arkansas, one caught in 2002 at Lake Ouachita (Garland County) weighed 26.7 kg (58 lbs., 14 oz.).

Grass carp inhabit quiet freshwater habitats, such as lakes, ponds, pools, and backwaters of large rivers, and tend to spawn in large rivers with relative turbidity. However, grass carp appear to be tolerant of low levels of salinity and may occasionally enter brackish waters. Generally, these carp do not migrate over great distances and prefer to congregate in specific areas, although desperate migrants have been known to travel widely. Interestingly, fingerlings in small ponds have been reported to survive five months under heavy ice cover. Due to their physiological plasticity, grass carp can invade many different types of aquatic environs and can consume various food sources. Most often, grass carp feed on plant material, which was the reason for their initial introduction.

Common Carp
It is believed that the common or European carp (Cyprinus carpio) evolved in the Caspian Sea and migrated naturally to the Black and Aral seas, east to eastern mainland Asia and west as far as the Danube River. C. carpio was thought to have been introduced from Europe and Asia into the United States in 1877 as a valued food source for European settlers, although there are some questions surrounding its introduction into the United States. Recorded from all states except Alaska, it was first introduced into Arkansas in the 1880s and became well established in the state’s waterways. Since its original introduction, C. carpio has been introduced throughout the United States intentionally and accidentally, allowing for its establishment across North America. Several genetic strains of C. carpio that are recognized by some as separate varieties include those bred specifically for aquaculture or to be used as ornamentals, commonly referred to as koi, leather carp, Israeli carp, and mirror carp. The “Israeli” variety was obtained by the AGFC in the late 1950s from fishery biologists at Auburn University to control aquatic vegetation.

The species generally inhabits lakes, ponds, and the lower sections of rivers (usually with moderately flowing or standing water) with significant amounts of aquatic vegetation, but is also known from brackish-water estuaries, backwaters, and bays. In the United States, C. carpio is more abundant in manmade impoundments, lakes, and turbid sluggish streams receiving sewage or agricultural runoff, and less abundant in clear waters or streams with a high gradient. In Arkansas, common carp inhabit a variety of aquatic sites, including reservoirs, upland streams, and lowland rivers and streams, and it is most abundant in soft-bottomed, weedy pools in clear or turbid water.

Common carps are omnivorous and possess an aggressive foraging behavior that uproots native plants as well as fish eggs. Larvae feed primarily on zooplankton, whereas the diet of adults is composed of organic detritus (primarily of plant origin), chironomids, small crustaceans, and gastropods. Common carp are known for being spot predators of bass and sunfish when sizes are appropriate.

This carp is a heavy-bodied fish that can weigh up to 34 kg (75 lbs.), but most individuals weigh 3.6 to 4.5 kg (8 to 10 lbs.) with a length of 30.5 to 63.5 cm (12 to 25 in.). The all-tackle world record C. carpio was caught in France in 1987 and weighed 35.5 kg (75 lbs., 11 oz.). The largest individual from Arkansas was from Lake Conway in 1985 and weighed 16.3 kg (36 lbs.). Some individuals have been recorded to live forty-seven years or longer. Their body coloration can be green, yellow, golden-brown, blue-green, or silver, with white or yellow ventrally. Common carp have two barbels on their upper jaw, their dorsal fin has seventeen to twenty-one rays, pectoral fin rays number fourteen to eighteen, and their anal fin possesses spiny projections with four to six rays.

Similar to their counterparts, this carp is an aggressive fish known for consuming natural resources to the point of depletion. Common carp release phosphorus in their waste, which increases algae growth, which in turn reduces the quality of life for native fish and plant species, as well as their populations. Turbidity is increased due to regular rapid movements of C. carpio disturbing sediment.

Common carp generally begin to spawn in April and continue until June, with some variation in duration in warmer climates. Females lay eggs in water one to four feet deep under vegetation with a clutch size ranging from 100,000 to 500,000 eggs. Larvae eat zooplankton and small crustaceans near the hatching area until they reach a length of one to four inches.

Studies have indicated that C. carpio may destroy aquatic macrophytes directly by uprooting or consuming the plants, or indirectly by increasing turbidity and thereby reducing much needed light for photosynthesis. Common carp have also been noted to have adverse effects on biological systems including destruction of vegetated breeding habitats used by both fish and birds. They also stir up the bottom substrate during feeding, resulting in increased siltation and turbidity. This feeding behavior also destroys rooted aquatic plants that provide habitat for native fish species and food for waterfowl.

Very little has been done to manage populations of common carp because they are so ubiquitous and have been established in the United States for more than a century. Further spread of common carp can be prevented by disposing of unused bait and by never releasing captives into new waters.

Silver Carp
Silver or Asian carp (Hypophthalmichthys molitrix) are native to the major Pacific drainages of eastern Asia from the Amur River in far eastern Russia south through much of the eastern half of China to the Pearl River, possibly including northern Vietnam. They were first brought into the United States in 1973 when a private fish farmer imported them into Arkansas to stock fish farms in the state. Stocking this carp increased by the mid-1970s due to six state, federal, and private facilities importing the fish, as well as being stocked in four municipal sewage lagoons. The silver carp was thought to be ideal for phytoplankton control and as a food source. However, by the 1980s, there were instances of H. molitrix in natural waters of Arkansas (Arkansas and White rivers), and later from the Mississippi River from accidental escapes. The occurrence of H. molitrix in the Ouachita River (Red River system) in Louisiana was likely the result of an escape from an aquaculture facility upstream in Arkansas. They have now spread and migrated throughout the large rivers of the Mississippi River basin and are able to reproduce successfully in off-channels and backwaters. Silver carp occur in the Arkansas and Red rivers of Oklahoma and the Arkansas, Mississippi, Red, St. Francis, and White rivers (and some of their tributaries) in Arkansas. By 2020, H. molitrix could be found in freshwater ponds, sewage ponds, and eutrophic ponds in sixteen states, including Hawaii.

In Arkansas in the early 1980s, commercial fishermen caught 166 silver carp from seven different sites; however, during an intensive 1980–1981 survey to determine the distribution and status of bighead and silver carp in the state’s open waters, AGFC personnel were not successful in collecting any additional specimens. However, there is no concrete evidence of natural reproduction in Arkansas waters.

Silver carp can be identified by their characteristic low-set eyes situated far forward and a large upturned mouth (without teeth on jaws but with pharyngeal teeth) lacking barbels. The silver carp is a deep-bodied fish that is laterally compressed. They are silvery in color when young, and when they get older they fade from a greenish color on the dorsum to silver on the venter. They possess tiny scales on their body, but the head and the opercles are scaleless. The anal fin has twelve or thirteen rays, the pectoral rays number fifteen to eighteen, and there are eight dorsal rays.

The silver carp looks very similar to another invasive Asian carp, the bighead carp (Hypophthalmichthys nobilis). However, H. nobilis has a keel on the venter that extends only partway to the head and has dark blotches along the dorsum, whereas the keel on H. molitrix extends all the way back to the head. In addition, H. molitrix possess a smaller head and mouth. Juvenile silver carp can be difficult to distinguish from other native species of bait fish, like gizzard shad (Dorosoma cepedianum). Silver carp are heavy-bodied fish that can generally weigh up to 27.2 kg (60 lbs.). The all-tackle world-record silver carp was caught in Korea in 2006 and weighed 32 kg (70 lbs., 8 oz.).

Silver carp are aggressive and are capable of consuming up to half of their body weight on a filter-feeding diet consisting primarily of phytoplankton, but they are also known to ingest zooplankton, bacteria, and detritus. They are able to out-compete native fish populations for resources with their foraging abilities and aggressive behaviors. Native species such as freshwater mussels, larval and adult fish such as paddlefish (Polyodon spathula), bigmouth buffalo (Ictiobus cyprinellus), and D. cepedianum are at greatest risk of being out-competed due to overlap in diet. These fish are also known for their ability to leap several meters out of the water when startled by boat motors; they sometimes land in boats, causing injury to people on board. The true impact of this species is difficult to predict because of its place in the food web.

In terms of reproduction, H. molitrix reach maturity at three years, are capable of reproducing until they are ten years of age, and can live to be twenty years old. Spawning occurs from May to September, when they can be observed migrating upstream in groups of fifteen to twenty adults. A mature female can lay up to five million eggs per year. Eggs are laid in a stream containing enough current to transport the eggs downstream.

Management practices include laws that prohibit the sale, spread, or importation H. molitrix within the United States. If one is caught, however, the angler is permitted to release it back into the lake from which it was taken or use it as food.

Bighead Carp
Like the silver carp, Hypophthalmichthys nobilis (another Asian carp that some, at one time, considered to be Aristichthys nobilis) is an invasive, large-bodied, fast-growing, highly fecund, voracious-feeding fish rapidly colonizing North American waterways. They are native to the large rivers and associated floodplains of southern and central China. Bighead carp were first imported into the United States in 1973 by a private fish farmer in Arkansas who wanted to use them in aquaculture in combination with other phytophagous fishes to control populations of zoo- and phytoplankton, improve water quality, use as a food fish, and increase fish production in culture ponds. In 1974, the AGFC and Auburn University obtained stock to assess their potential benefits and impacts. The first record of a bighead carp, thought to have escaped from a fish farm, was collected in 1981 in Kentucky on the Ohio River just below Smithland Dam. The first open water record of H. nobilis in Arkansas was two specimens taken from the Arkansas River near Pine Bluff (Jefferson County) in 1986; however, as of the late 1980s, there had been no evidence of natural reproduction in the state. Natural disasters such as floods and potential human negligence have led to the escape of many more bighead carp over the years. Like H. molitrix, they are notorious for their ability to jump out of the water, and this carp is becoming more and more prevalent below dams and spillways of the Mississippi and other Midwestern rivers. Substantial efforts are being made to prevent their introduction into the Great Lakes. Both bighead and silver carp were found in Lake Chicot (Chicot County) in 2005, and by 2007, they had grown large enough to cause problems with boating and recreation on the lake. As a result, commercial fishing for those species was allowed beginning in 2017. By 2020, H. nobilis had been reported from twenty-three states, as well as some Canadian waters.

The bighead carp is characterized by having a stout, deep, and narrow body with tiny scales, a large head, small downward-facing eyes (often below the jaw angle), and large opercles. Its head has no scales, a large mouth with no teeth, and a protruding lower jaw. This carp can be identified by a smooth keel between the anal and pelvic fins that does not extend anterior of the base of the pelvic fins. Soft dorsal fin rays number eight (rarely nine), there are sixteen to twenty-one pectoral rays, and soft anal rays number thirteen (rarely fourteen). Bighead carp can reach weights up to 45 kg (100 lbs.) and lengths up to 120 cm (4 ft.). The all-tackle world record H. nobilis was caught in 2005 from Guntersville Lake, Tennessee, and weighed in at 40.8 kg (90 lbs.).

The bighead carp poses a great risk to novel ecosystems for several reasons: (1) it is a large, aggressive fish capable of out-competing native fish for resources, (2) it is an opportunistic feeder that consumes high quantities of zooplankton and phytoplankton, and (3) it is capable of rapid reproduction, laying up to thousands of eggs at one time.

Bighead carp are filter feeders that use their specialized gill rakers as screens to capture their prey. Their ventrally-positioned eyes also offer the fish the ability to see as it swims along the water surface raising food items. The diet of this species overlaps with that of other planktivorous species, such as fish and invertebrates, and to some extent with that of the young of virtually all native fishes. Bighead carp have the ability to deplete plankton stocks for native larval fishes and mussels.

Female bighead carp are capable of reaching sexual maturity at three years of age, while males can reach sexual maturity in two years. They are known to spawn only in large, turbulent rivers, and it is thought that a flood event is a primary spawning signal. In North America, fecundity can reach up to 1.6 million eggs. Bighead carp produce eggs that are semi-buoyant for several days before hatching and require current to keep them from sinking to the bottom.

The impact of this species in the United States is not adequately known, and managing bighead carp has proven to be a rather difficult task. Because they are planktivorous and attain a large size, they have the potential to deplete zooplankton populations. Such a decline in the availability of plankton can lead to reductions in populations of native species that rely on plankton for food, including all larval and some adult fishes, and native mussels (some of which are threatened or endangered). Adult fishes most at risk from such competition in the Mississippi and Missouri rivers are P. spathula, I. cyprinellus, and D. cepedianum.

Although both silver and bighead carp have been a staple in Asia for many generations, the potential for being an acceptable food fish in America is growing. One blind taste test was conducted by the University of Missouri, and the carp won handily over much more popular standard catfish. Another similar test was done and found that diners preferred the carp two-fold over catfish and tilapia, regardless of how they were cooked.

Black Carp
The black carp (Mylopharyngodon piceus) was first imported into the United States (at a private fish farm in Arkansas) in the early 1970s as a “contaminant” in imported grass carp stocks. By the 1990s, this species was being used in fish farms in several southern states to control pond snails, as a food fish, and as a biological control agent to combat the spread of the trematode yellow grub (Clinostomum marginatum) parasite in aquaculture ponds. During the same time period, it was reported that the number of M. piceus held by fish farmers and others in a few southern states totaled nearly half a million individuals, including both triploid (sterile) and diploid (fertile) genetic stock. Also at that time, privately owned aquaculture facilities, located in Arkansas and Missouri, each reportedly held more than 100,000 diploid and triploid M. piceus.

The native range of M. piceus includes most major Pacific drainages of eastern Asia from the Pearl River (Zhu Jiang) basin in China north to the Amur River (Heilong Jiang) basin of China and far eastern Russia and possibly to the Honghe or Red rivers of northern Vietnam. This species can be found in rivers, streams, or lakes but requires large rivers to reproduce.

The first known introduction of M. piceus into open waters was recorded in 1994 in Missouri when several black carp along with several thousand bighead carp reportedly escaped into the Osage River (Missouri River drainage) when high waters flooded hatchery ponds at an aquaculture facility near the Lake of the Ozarks. Flooding of aquaculture facilities and associated numbers and types of escaped fishes are to blame for the spread of this carp. In addition, there is also risk that black carp may be spread by other means. For example, as early as 1994, hundreds of young M. piceus were accidentally included in shipments of live baitfish sent from Arkansas to bait dealers in Missouri. Black carp have been reported from Arkansas, Missouri, Illinois, and Mississippi.

The black carp is a blackish-brown fish with blackish-gray fins and an elongated and laterally compressed body. They average more than 0.9 m (3 ft.) in length and 15 kg (33 lbs.) in weight, but based on Asian records, large adults may be more than 1.5 m (4.9 ft.) in total length and 70 kg (154 lbs.) or more in weight. The all-tackle world record M. piceus was collected in 2000 in Japan and weighed 18.5 kg (40 lbs., 12 oz.). Individuals of the species are known to live for at least fifteen years. The species closely resembles C. idella in overall body shape, large scales, size, and placement of fins. However, in contrast, M. piceus are slightly darker in coloration (not black), and their pharyngeal teeth (throat teeth) are molar-like and large.

The black carp is primarily a bottom-dwelling molluscivore. Juveniles feed on zooplankton and insect larvae, while adults feed on benthic invertebrates such as snails and mussels, so different fauna may become exhausted. Individuals may consume as much as twenty percent of their body mass in one day. So there is high potential that M. piceus can harm native aquatic communities by feeding on, and reducing, populations of native mussels and snails, many of which are protected species. Black carp also have the potential to rearrange benthic communities by direct predation and removal of algae-grazing snails and native mussels. Since the lifespan of the M. piceus is thought to be over fifteen years, sterile triploid black carp in the wild are expected to persist many years and therefore have the potential to harm native mollusks by way of predation.

Black carp are explosive broadcast spawners, and reproduction takes place in late spring and summer in riverine habitat when water temperatures and/or water levels rise. Females are capable of releasing hundreds of thousands of eggs (in one brood) into flowing water, which then develop in the pelagic zone. Following fertilization, the eggs become semi-buoyant and hatch in one to two days, depending on water temperatures. They become sexually mature at four to six years after which they migrate back to their spawning grounds.

Because the black carp has been used in the aquaculture industry for decades, its removal in the near future in an economically feasible method seems very unlikely. However, researchers, who are worried about an escape/colonization event, have urged fish farmers to use sterile triploid M. piceus so escapes will not lead to a breeding population

There is a tremendous diversity of parasites reported from North American C. carpio but only a few from C. idella, including S. acheilognathi and the copepod, Lernaea cyprinacea. A nematode, Eustrongylides sp., was reported from a grass carp from a fish farm in Pulaski County. Information on parasites of H. molitrix, H. nobilis, and M. piceus are based on Euro-Asian records, from China, Russia, and Poland.

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Chris T. McAllister
Eastern Oklahoma State College