Date of this Version
Carps of the family Cyprinidae, the largest family of freshwater fishes in the world (Nelson 1994), have long been introduced beyond their native ranges, a practice that continues today. Although carps have been introduced for several centuries, the widespread introduction of the genus Hypophthalmichthys, the bigheaded carps, is a relatively recent phenomenon. All three recognized species of Hypophthalmichthys—H. nobilis, in North America referred to as Bighead Carp; H. molitrix; Silver Carp; and H. harmandi, Largescale Silver Carp—are native to fresh waters of eastern Asia. Largescale Silver Carp have been introduced elsewhere in west-central Asia as a hybrid with Silver Carp but are not known to have been brought to North America. Both Bighead and Silver carps have been introduced to many countries, including the United States, for uses in aquaculture production of food fishes and biological control of plankton in aquaculture ponds, reservoirs, and sewage treatment lagoons.
Bighead and Silver carps were first imported into the United States in the early 1970s. Soon after, both species were being used in research projects and were stocked into wastewater treatment lagoons and aquaculture ponds in several states without regard to their potential effects on the ecosystems to which they were introduced or on the species inhabiting them. Bighead and Silver carps escaped confinement during flood events and are now well established with reproducing populations in much of the Mississippi River Basin. The introduced range of both carps in the United States continues to grow. Based on the climate where these fishes are native, Bighead and Silver carps might eventually be found in many of the flowing waters of the United States.
The escape of Bighead and Silver carps during evaluation as phytoplankton biological control organisms in commercial aquaculture ponds and sewage treatment facilities has left a legacy that could affect native fish populations within the Mississippi River Basin for decades to come. Populations of these carps in parts of the Mississippi River Basin appear to be increasing exponentially. If food resources become limiting, Bighead and Silver carps may compete with native planktivorous fishes, like Gizzard Shad, Dorosoma cepedianum, Bigmouth Buffalo, Ictiobus cyprinellus, and Paddlefish, Polyodon spathula. In addition to continuing to spread farther in the Mississippi River Basin by natural spread, the spread of Bighead and Silver carps could be aided by transportation of fishes caught for live bait, by livehaulers, the live seafood industry, and by those practicing prayer animal releases (practiced as a form of prayer by those whom believe that merits can be accrued by freeing captive animals into the wild).
Although Silver Carp are not known to be cultured for marketing purposes in the United States now, Bighead Carp continue to be cultured in some states. Markets exist for live Bighead Carp in ethnic markets in the United States and southern Canada requiring transport in live haul trucks. Silver Carp have not been as prominent in the live food fish trade as Bighead Carp because they are not available from aquaculture and because they are more fragile to handle and transport alive. However, wild-caught Silver and Bighead carps are occasionally encountered in live markets.
The purpose of this document is to present a summary of the biology and distribution of the three species of Hypophthalmichthys. For each species, information is included as follows: (1) taxonomy and distinguishing characteristics; (2) native range; (3) habitat preferences; (4) migrations and local movements; (5) biology and natural history (including temperature and salinity tolerances, reproductive biology, feeding habits, growth rate and longevity, and response to physical stimuli); (6) diseases and parasites; (7) human uses of Hypophthalmichthys (including harvest from reservoirs and other water bodies, culture, control of algae, removal of excess nutrients, and production and growth of other fishes); (8) history of introductions around the world and the United States; (9) potential range in the United States; (10) population and distribution control measures; and (11) state regulations.
Although most of the information in this document is supported by citations from peer-reviewed scientific literature, we have relied on personal observations and personal communications for some information, particularly the biology of Bighead and Silver carps in the United States. A variety of biological research is in progress on these fishes in the Mississippi River Basin, but much of the information from this research has not yet been vetted through peer-reviewed journals. We have minimized reliance on unpublished information to the greatest extent possible.
Also included is an evaluation of the organism risk potential of each species of Hypophthalmichthys in the United States using the Generic Nonindigenous Aquatic Organisms Risk Analysis Review Process. This risk assessment process uses both the probability of establishment and the consequences of establishment to determine the overall organism risk potential in the United States. This document is limited to the ecological effects and consequences of Hypophthalmichthys in the wild. The economic benefits of the continued culture and marketing of Hypophthalmichthys are beyond the scope of this document and are being evaluated by the U.S. Fish and Wildlife Service. Department of Fisheries and Oceans is also conducting a risk assessment on Asian carps of the genera Ctenopharyngodon, Hypophthalmichthys, and Mylopharyngodon in Canada.
Although we provide some discussion on the culture of these carps, we do not treat it in detail. For further information on the culture methods of Bighead and Silver carps, see Chen et al. 1969; Pagan-Font and Zimet 1979; Chung et al. 1980; Tsuchiya 1980; Rothbard 1981; Dupree and Huner 1984; Jhingran and Pullin 1985; Jennings 1988; Li and Mathias 1994; Li and Senlin 1995; Opuszynski and Shireman 1995; and Xie 2003.