Cyprinidae - Carps and Minnows
Although specimens are collected periodically, self-sustaining populations seem to be lacking in Florida. Releases seem to have been made by aquarists, ornamental-pondfish hobbyists, and anglers (as excess bait). Escaped individuals are from culture facilities, including state and federal hatcheries where the goldfish is used as forage for game fishes. Lack of cold winter temperatures in Florida may interfere with gonad maturation, preventing natural reproduction.
Grass Carp (Ctenopharyngodon idella). The grass carp, also called white amur, is native to the middle and lower Amur River (as far north as Blagoveshchensk, East Russia, Asia, the Sungari and Ussuri rivers and Lake Khanka, in eastward flowing rivers of the People's Republic of China south to Guangzhou, Kwangtung Province [Berg 1949a]). This species is established in the lower Mississippi River near Eudora, Chicot County, Arkansas; near Simmesport, Avoyelles Parish, Louisiana; near St. Francisville, West Feliciana Parish, Louisiana (Conner et al. 1980); and in the Trinity River, Texas (Robert Howell,Fish Biologist, Department of Texas Parks and Wildlife, Austin, Texas, personal communication). As of 1977, specimens of grass carp have been collected in the wild in Alabama, Arkansas, Florida, Georgia, Maryland, Michigan, Missouri and New York. Unconfirmed reports indicate the presence of this fish in the Mississippi River in Wisconsin and Minnesota and in the Missouri River in Kansas and Nebraska as far upstream as Gavins Point Dam near Yankton, South Dakota (Courtenay et al. 1986).
Introduction of the grass carp into the United States as an aquatic-plant control agent was first recommended by Swingle (1957). The grass carp was first imported by the U.S. Fish and Wildlife Service Fish Farming Experimental Station (Stuttgart, Arkansas) from Malaysia and by the Auburn University (Auburn, Alabama) from Taiwan in 1963 (Guillory and Gasaway 1978). It was subsequently distributed to research agencies or companies in 11 states (Provine 1975). As predicted by Stanley et al. (1978), grass carp became established in the lower Mississippi River (Connor et al. 1980). The age of the adults taken from the Mississippi River indicated that they were from the 1966 age-class (Guillory and Gasaway 1978), meaning the adults were hatched only 3 years after the species was introduced into this country. The grass carp is becoming a major species in the lower Mississippi River basin.
Guillory and Gasaway (1978) summarized the distribution and the history of the grass carp in the United States as of 1976. The species was first brought into Florida as a weed control agent in the early 1960s (Sutton and Vandiver 1986). Disagreement on whether environmental conditions in Florida allow the species to reproduce has been considerable. Now, reproduction is unlikely because the transport of fertile, diploid grass carp into Florida without a permit from the Florida Game and Freshwater Fish Commission is illegal. Adult grass carp have been taken from the open waters of Florida and are probably fishes that escaped from efforts to control nuisance aquatic weeds rather than the result of natural reproduction.
Several biological synopses have been completed on the grass carp (Shireman and Smith 1983; Smith and Shireman 1981). A review of the literature does not provide any evidence that the species can reproduce in standing bodies of water; in fact, reproducing populations have been found only in large river systems. After reviewing locations and spawning conditions in the grass carp's native range and where it had been introduced and became established, Stanley (1976) concluded that grass carp would become established in the Mississippi River in 1978 or 1979. Requirements for natural spawning of grass carp, such as suitable water temperature, water level, spawning site, water velocity, length of river, and water quality were discussed by Stanley et al. (1978). Fish egg and larvae samples from the Mississippi River in 1975 contained grass carp specimens and revealed spawning in the lower river (Conner et al. 1980). Zimpfer et al. (1987) obtained close correlations when they compared spawning conditions in the Mississippi River when grass carp eggs and larvae were found there with the conditions in other major rivers in the world where the species is established. These researchers also emphasized the location of suitable feeding areas at correct distances downstream from spawning grounds to provide necessary nursery grounds. By 1983, grass carp were 23% of the ichthyoplankton catch and were second only to the freshwater drum (Aplodinotus grunniens) in total abundance (Zimpfer et al. 1987). Although the species is now well established in the Mississippi River and entering the commercial catch, no harm has yet been attributed to the introduction of this species.
Introductions of nonindigenous parasites with the grass carp into the United States and Florida were discussed by Riley (1978). Although he found no evidence that exotic parasites had been introduced with grass carp into Florida, he found that grass carp had become infected with a native parasite that previously had never been reported. He found that no examination of grass carp had been made before they were introduced into Florida and recommended that this species should be quarantined and inspected for parasites and diseases before it is imported into Florida. The introduction of grass carp was responsible for the introduction and spread of a fish tapeworm (Bothriocephalus opsarichthydis) to other cyprinid fishes in the United States (Hoffman and Schubert 1984).
The rationale for importation and introduction of this fish was for its use as a biological control agent of aquatic weeds, many of which are exotic species. The concern about using the grass carp for the control of aquatic vegetation is centered around whether the species could reproduce in the wild, overpopulate, and remove all vegetation. Research at the Fish Farming Experimental Station at Stuttgart, Arkansas, to develop year classes of pure female grass carp that could be considered sterile if no adult male grass carp are in the water. Use of monosex populations, usually all females, was short-lived because the fishes were fertile and the identification of sex was difficult when the fishes were young, facilitating the accidental introduction of males and reproduction. Early attempts to develop a sterile grass carp concentrated on the development of a hybrid between male bighead carp and female grass carp (Allen and Wattendorf 1987). Studies revealed the hybrid fry had lower survival and slower growth rates and consumed less vegetation (Shireman et al. 1980 and 1983), and its habit of schooling near the surface made it vulnerable to predation by birds. As a result, the hybrid was dropped from further consideration as a control agent. In the early 1970's, methods were developed to produce pure (unhybridized) grass carp triploids (Purdom 1983). Application of this procedure was simple after the technique was developed. The fertilized egg has to be shocked by either extreme cold or pressure changes to inhibit the second maturation division of meiosis of the fertilized egg and cause retention of an extra set of chromosomes (Allen and Wattendorf 1978). Correct application of the technique produces almost 100% triploids. Verification of triploidy is easy with a Coulter Counter (Wattendorf 1986). Triploid grass carp are sterile and similar to diploids in their ability to consume nuisance vegetation. Wattendorf and Shafland (1983) studied consumption of hydrilla in Florida with triploid hybrid grass carp. Most states, including Florida, require use of verified triploid grass carp (Allen and Wattendorf 1987).
One major environmental concern has been the effect of grass carp on the ecology of lakes and waterfowl (Gasaway and Deda 1977; Gasaway et al. 1977, 1978). In January 1976, the Waterways Experimental Station, U.S. Army Corps of Engineers, initiated a study with monosex grass carp on Lake Conway near Orlando, Florida. To avoid escape of the grass carp from the lake, the corps purchased monosex grass carp from the United States Department of Interior Fish Farming Experimental Station in Stuttgart, Arkansas, and introduced them into the lake after 1 year of baseline information had been collected on the lake's water and sediment chemistry, the plankton and benthic invertebrates, fishes, waterfowl, aquatic mammals, herpetofauna, aquatic macrophytes, hydrology, and nutrient sources (Lazor 1983). The study also included a computer model to simulate the response of the lake and its organisms to introduction of the grass carp (Theriot and Decell 1978). The study on this five-pool lake system was completed after the analysis of data from the 3 post-stocking years. The stocking rate of 7-12 fishes/ha reduced the three most common aquatic plants (Hydrilla, Nitella, and Potamogeton) by 90%. Vallisneria, the fourth most abundant plant, increased slightly because of the reduced competition from other plants and because it is not a preferred food of grass carp. The abundance of small fishes that lived in the vegetation dropped, and the larger fishes such as the largemouth bass (Micropterus salmoides) moved into deeper water and gained weight from eating the smaller fishes that lacked cover. The angler success doubled. The two most common ducks, the ring-necked duck (Aythya collaris) and the American coot (Fulica americana), increased their intake of amphipods. Phytoplankton species were significantly fewer in all pools during the latter part of the study. The dominance of Chorophyta and Chrysophyta in summer were eliminated; Cyanophyta (blue-green) algae replaced them and remained high all year. Except in one pool, phytoplankton was significantly greater in all pools during the middle 2 years of the test. The reduction of the vegetation was followed by the reduction of periphyton. The total number of zooplankton decreased throughout the entire study, although the mean number of species per sample did not decline. Sediment and water chemistry and the populations of benthic macroinvertebrates, herpetofauna, waterfowl, and aquatic mammals seemingly were not directly affected by the introduction of the grass carp. Other factors such as state-wide reduction in waterfowl, lack of normal rainfall, falling water levels, and increased residential development masked small changes. The most pronounced environmental change was the increase in phytoplankton abundance. Independent removal of vegetation by private land owners around the lake complex also made it difficult to fully evaluate the effects of the grass carp.
A recent symposium in Florida (Shireman 1995) summarized the present status of the grass carp in Florida and its use as a weed control agent in both large and small bodies of water. Noble et al. (1986) discusses the consideration that need to be made when considering its use in large open systems.
Common Carp (Cyprinus carpio). The native range of the common carp encompasses the basins of the Black, Caspian, and Aral seas and possibly eastern Europe, the Volga River, the rivers flowing into the Pacific Ocean and eastern Asia from the Amur River southward to Burma (Berg 1949a). Misik (1958), Balon (1974) and others suggested that the species first appeared in Asia Minor and in the basin of the Caspian Sea and spread from there into western Europe and eastward to China (Courtenay et al. 1986).
Self-sustaining populations of common carp are in the 48 contiguous states (Allen 1980) and in the provinces of British Columbia, Manitoba, Ontario, Quebec, and Saskatchewan (Scott and Crossman 1973). In North America, the greatest population densities of this fish are in the midwestern states. A citizen is responsible for the first introduction into North America via the Hudson River in New York in 1831 (DeKay 1842). In 1872, five carp were imported from Germany and released in a pond in the Sonoma Valley, California (Moyle 1976). In May 1877, the U.S. Fish Commission imported 338 specimens from Germany and subsequently began distributing this species for culture and for introduction to applicants throughout the United States and Canada until 1896 (Laycock 1966; Scott and Crossman 1973; Baird 1879).
The common carp has been taken from many bodies of water throughout most of Florida, even as far south as Lake Okeechobee where it was probably introduced as bait by anglers. It is supposedly established in only several river systems including the Apalachicola and Ochlocknee rivers in the panhandle of Florida, and has been recorded in these systems for several years. No studies have been conducted to determine whether its introduction has had adverse impacts. Advantages and disadvantages from the introduction of the common carp into the United States are discussed in detail in a group of published papers (Cooper 1987). Efforts to control nuisance populations, particularly in the midwestern United States, have cost millions of dollars. In some national wildlife refuges, the harmful effects by common carp on rooted vegetation have been the most serious environmental problem.
The greatest harm by the common carp in some areas of the country is from its habit of uprooting aquatic vegetation and muddying the water, which covers the nests of spawning fishes, and increasing turbidity. This reduces light penetration for a healthy aquatic plant population (Taylor et al. 1984).
In some midwestern states such as Iowa, carp are taken from state waters by large nets and sold in fish markets in New York and in southeastern Florida. Interest in raising this species in aquaculture facilities to supplement the wild commercial catch is also rising, and efforts have been made to promote it as a game species. This species is still considered an undesirable introduction by most environmentally oriented professionals.
Silver Carp (Hypophthalmichthys molitrix). Silver carp were first imported into the United States in 1972 under an agreement of maintenance with the Arkansas Game and Fish Commission (Shelton and Smitherman 1984). Shelton and Smitherman (1984) summarized the early work on this species in the United States. The silver carp was imported as a potential food fish and for its ability to filter phytoplankton. It has also been used as a biological control agent to reduce phytoplankton populations in tertiary-water treatment systems. Courtenay and Williams (1992) reported that in the early 1970's, this species was taken from open waters in Arkansas where it apparently had been released from an aquaculture facility. They stated that the silver and the bighead carp are seriously considered for aquaculture in several states. Although the silver carp is presently cultured in Florida, releases or establishments in the state have not been recorded. Like the grass carp, this species is not expected to establish itself in Florida.
Bighead Carp (Hypophthalmichthys nobilis). The bighead carp was first imported into the United States in 1972 (Cremer and Smitherman 1980) because of its potential as a food fish. Shelton and Smitherman (1984) summarized the early research into this species in the United States. The bighead carp feeds primarily on zooplankton and has been considered as an agent for tertiary-water treatment systems. It is presently cultured in Florida but is not considered established. A biological synopsis on this species was recently completed (Jennings 1988). Like the grass carp, it is not expected to become established in Florida however where its use may be beneficial, sterile bighead carp may be a better choice.
