Fishes (P.L. Fuller)

Overview

A total of 231 fish species have been introduced into the 11 states within USFWS Region 4. Of these, 133 are species native to the United States but have been transplanted outside their native range (Appendix A; Table 1), and 98 are species introduced from other countries (exotic) (Appendix A; Table 2). Eighty-two percent of the native transplants and 49% of the exotic species have resulted in established populations (Appendix B).
 

Figure 1. Number of fish species introduced into each state (Fuller et al. 1999).
 

Florida has more species of fishes introduced than any of the other states in USFWS Region 4 (Appendix B and Figure 1). The majority of these introductions are aquarium species that were either released by hobbyists or escaped tropical fish farms.
 

Figure 2.  Number of fish species introduced into regional drainages (Fuller et al. 1999).
 

When divided into regional drainages, the South Atlantic-Gulf has the greatest number of introduced fish species of any of the regional drainages in the country (Figure 2).

Numbers of Introduced and Established Species in Each State

In the Southeast, Florida and North Carolina have the most species introduced and the most species established (Figure 3).  However, the dominant pathway in each state is different (Appendix B). The majority of Florida's introductions are related to the aquarium trade; North Carolina's are the result of stockings, mainly for sportfishing.  An average of 72% of all fish species introduced in the Southeast become established (Appendix B). Puerto Rico's high establishment rate may be artificially high due to the lack of reporting of failed introductions.
 

Figure 3.  Total number of species introduced to each state.
 

Tables 1 and 2 in Appendix A contain a complete list of species introduced into each state.
 

Figure 4.  Number of native fish species transplanted in each state.
 

North Carolina and Georgia are the two states in Region 4 with the highest number of native transplants (Figure 4).  North Carolina has a large number of minnow species that are thought to have been introduced outside their native range as the result of bait releases. A small portion of the Tennessee drainage falls within these two states. The Tennessee drainage has many species that differ from the other drainages in these states.  Many of the native species have been moved between the Tennessee drainage and into other drainages in these states. Puerto Rico has no native fish fauna but has been stocked with sport fish from the mainland – largely bass, sunfish, and bullheads. In the Southeast, an average of 82% of native species transplanted outside their native range became established (Appendix B).
 

Figure 5.  Number of exotic fish species introduced into each state.
 

The state of Florida has, by far, the most exotic fish species introduced and established (Figure 5).  In the Southeast, roughly half of all the exotic species introduced became established (Appendix B and Figure 5).  A list of species and their status is provided in Appendix A: Table 2.

Introduction Trends Over Time

Introductions in the Southeast mirror the nation-wide trend of an increase in the number of species introduced since the 1950s (Figure 6).
 

     Figure 6.  Cumulative number of fish species introduced
into the United States (Fuller et al. 1999).
 

Most of the increase in the Southeast has occurred since the 1970s (Figure 7). The total number of species that have been introduced in the Southeast is 400% higher in 2000 than it was in 1950.  Much of this is the result of aquarium fish introductions in Florida.  These are attributable to the growing human population in the state and the increased interest in aquariums as a hobby in recent decades.
 

Figure 7.  Cumulative number of fish species introduced into the Southeast by decade.

Pathways

The major pathway of fish introductions for all states in Region 4, except Florida, is intentional stocking for sportfishing or forage (Appendix B). Species stocked in these states include: various species of sunfish and bass, pike, muskellunge, bullheads, catfish, yellow perch, walleye, sauger, white bass, and several species of trout and salmon (Appendix A; Table 1). The dominant pathway in Florida is the release or escape of animals associated with the aquarium trade.

Nationally, stocking for sport or forage is the most dominant pathway for introduced fishes. The aquarium trade is next and accounts for ~25% (Figure 8). Bait releases are believed to be responsible for another ~16%.  Fewer introductions are attributable to ballast water releases, stocking for biocontrol, stocking of endangered species for conservation purposes, and miscellaneous methods such as canal connections, research releases, and escapes from aquaculture that are not related to aquarium fishes.
 

Figure 8.  Pathways of fish introductions in the United States (Fuller et al. 1999).
 

In the Southeast, stocking, bait release and aquarium releases (or escapes from tropical fish farms) are of roughly equal importance (Figure 9). However, the proportion of aquarium releases in the Southeast is heavily skewed by the dominance of this method of introduction in Florida (Figure 10).
 

Figure 9.  Pathways of fish introductions in the Southeast.

Figure 10. Pathways of fish introductions in Florida.
 

An analysis of the three main pathways in the Southeast shows that although all three have increased dramatically in strength (Figure 11). This analysis also shows that the dominant pathway has shifted from stocking in the late 1800s and early 1900s, to introductions associated with the aquarium hobby (releases and escapes from tropical fish farms) in recent decades. However, this shift is heavily influenced by the number of aquarium introductions in Florida. If Florida were excluded, stocking would be the dominant pathway in the Southeast just as it is nationwide.
 

Figure 11. Number of new species introduced via the three
major pathways over the course of the last 150 years.

Geographic Origin of the Introduced Species

The majority of species introduced in the Southeast are native to the United States but transplanted outside their native ranges (Figure 12). Included are various species of minnows, sunfishes, bullheads and catfishes, salmon, and darters. Of the exotic species, most are associated with the aquarium trade.  South America is the source region that provides the largest number of species to the Southeast. These include several groups of catfishes (Callithyidae, Doradidae, Loricariidae, Pimelodidae), cichlids, and characins (pacus, piranhas, tetras) from South America. Asia is the next largest contributor to the Southeast, and is the source of the introduced barbs, grass carp Ctenopharyngodon idella, bighead carp Hypophthalmichthys nobilis, silver carp H. molitrix, common carp Cyprinus carpio, and Asian swamp eel Monopterus albus.  Some species belonging to the family Cichlidae, such as the blue tilapia Oreochromis aureus, and Mozambique tilapia O. mossambicus, have come from Africa.  Other cichlid species and species of livebearers such as the mollies, platys, and swordtails originated from Central America. Only a few species have come from Europe, and all were introduced as either sport fish or bait.  These include the brown trout (Salmo trutta), tench (Tinca tinca), and rudd (Scardinius erythrophthalmus).
 

Figure 12. Geographic origin of introduced fishes in the Southeast.
.

Figure 13 shows the continental origin of fish species introduced in 50-year increments. Although North America (the United States) has always been the major source of introductions, those from other continents have grown in recent decades.
 

Figure 13. Origins of introduced fish species through time.

Figure 14. Composition and origin of introduced fishes in southeastern states.  Introduced = native to the US, but not to that state; Native and Introduced = native to part of the state, but introduced outside its native range in the state; Exotic - species not native to the US; Hybrids - stocked hybrids (wipers, tiger muskie, etc.)
 

When the origin of introductions are examined on a state by state basis, the predominant origination varies (Figure 14). As previously mentioned, Florida has a high number of foreign species introduced.  These are primarily species from the aquarium trade that either escaped tropical fish farms or were released by hobbyists. North Carolina has a high percentage of species native to the state but moved outside of their native range (usually across the Appalachian Divide).  It is believed that this large percentage is the result of numerous bait releases.  Georgia has numerous species that have been moved from Atlantic to Gulf Slope drainages or visa versa. Tennessee includes several species stocked from other states.  The state also contains the Tennessee and Ohio drainages, each with a unique fauna. Some of these species have been moved between the two drainages. Similarly, the state of Alabama has experienced faunal interchange between the Gulf and Tennessee drainages.

Vulnerable Areas

As a general rule, lakes and reservoirs near metropolitan areas throughout the Southeast are areas vulnerable to introductions. These waters are the most likely to be stocked with sport and forage fish for recreational fishing for nearby city residents. Also, they are the waterbodies most likely to receive unwanted pet and aquarium releases.

Other specific examples of vulnerable areas include:

• Florida - South Florida, Tampa (Figure 15).  Most of the tropical fish farms are in the Tampa region.  South Florida already harbors a large number of species, and is hospitable to many tropical species because of the climate.  These regions are also densely populated with humans, making introductions more likely.  South Florida, in particular, is home to a variety of ethnic groups that often import foods of their native homelands.  Some of these are sold live in markets and can escape or be released into the wild.
   

Figure 15. Number of fish species introduced into Florida drainages.
 

• Georgia - Atlantic slope drainages have gained a number of transplants from across the Appalachian Divide.  Reservoirs surrounding the Atlanta area are also vulnerable because of the large human population that makes recreational use of them.
   
• Kentucky - reservoirs on the Cumberland and Tennessee Rivers.
   
• Tennessee - reservoirs on the Cumberland and Tennessee Rivers.
   
• The Mississippi River acts as a conduit to allow the spread of large-river species such as the bighead, silver, common, and grass carps.

Updates on Recent Introductions

Asian Swamp Eel Monopterus albus

This species is native to Asia, from northern India and Burma to China, and perhaps to Asiatic Russia, Japan, the Indo-Malayan Archipelago (Bailey and Gans 1998) and northeastern Australia (Merrick and Schmida 1984).  This eel reaches a length of up to 100 cm.

The Asian swamp eel was first discovered in the Southeast in Georgia. It was first collected in 1996 (although it was likely present since 1990 or before) from three ponds at the Chattahoochee Nature Center in Roswell, Fulton County, Georgia (Starnes et al. 1998).   The population in this location was probably the result of an aquarium release.

In Florida, the Asian swamp eel occurs in the Miami (three distinct populations) and Tampa (one population) areas (L.G. Nico, unpublished data). One population of particular concern is immediately adjacent to the Everglades National Park. Its introduction into Florida may have resulted from an aquarium release, a fish farm escape or release, or a combination of all of the above (L.G. Nico, personal communication).

The impacts of these eels are largely unknown. Because they are generalized predators, this species is a potential threat to native fishes, frogs, and aquatic invertebrates. In both Georgia and Florida there is concern that the species will spread to adjacent water bodies. The Georgia impoundments where this eel has been taken are connected to the Chattahoochee River.  Although it has not been collected from the Chattahoochee River, its occurrence there would not be surprising because the impoundments have been heavily flooded since the population was discovered there. The Miami populations are in a network of interconnected canals and are expanding their range through these canals.

This eel is a capable of living out of water for a considerable length of time (Day 1958). The Georgia population has shown some cold tolerance, as evidenced by having survived air temperatures below freezing and ice cover over the pond they inhabit (Starnes et al. 1998). The distribution, biology, and impacts of Florida populations are being investigated by USGS Florida Caribbean Science Center researchers in conjunction with university biologists.

Flathead catfish Pylodictis olivaris

The flathead catfish is native to the Mississippi, Ohio, and the western Gulf drainages.  It has been introduced both legally and illegally for sport fishing. The state of Georgia is now trying to control them in the Altamaha River, and has taken an enormous amount of flathead biomass out of the river.

Biologists have noted that native sunfish, madtoms, and bullheads disappear in areas where the flathead is introduced. This species may also be a factor in the decline of the Gulf sturgeon Acipenser oxyrhynchus desotoi through predation on young fish.

Brown hoplo Hoplosternum littorale

The brown hoplo is native to tropical America and is widespread in South America east of the Andes and north of Buenos Aires (Reis 1997).

This species is established in peninsular Florida (Nico et al. 1996) and has recently expanded its range into several new drainages within the state (L.G. Nico, unpublished data).  The first population was discovered in ditches of the Indian River lagoon system in Florida in late 1995 (Nico et al. 1996). Recently, populations have been found in the St. Johns and Kissimmee River drainages (L. G. Nico, unpublished data).  It is unknown how the species was introduced.

Impacts of this species are largely unknown. In several Florida waterbodies the brown hoplo is locally abundant. Because it feeds heavily on benthic invertebrates and detritus, the species may be causing significant changes in food web structure, negatively impacting native invertebrates, and competing with native fishes for food (L.G. Nico, unpublished data). It is capable of breathing air and can tolerate a wide range of environmental conditions (e.g., fresh and brackish waters). There is concern that it will eventually invade many natural freshwater wetlands, and coastal marshes in Florida (Nico et al. 1996).

The distribution, biology, and impacts of introduced populations in Florida are being investigated by U.S. Geological Survey researchers.

Red shiner Cyprinella lutrensis

In degraded streams in Georgia, introduced red shiners have become one of the most abundant species (Devivo and Freeman 1995). The red shiner was discovered in northwest Georgia in the upper Coosa River system in the early 1990s. In the past two years, red shiner populations have significantly increased in density and spatial occurrence.  There is particular concern the red shiner may hybridize with the threatened blue shiner Cyprinella caerulea; it is already massively hybridizing with the indigenous blacktail shiner C. venusta (N. Burkhead, pers. comm.).

The origin of most introduced red shiner populations can be attributed to bait releases; however, initial introduction is often followed by the species' rapid multiplication, dispersal, and aggressive colonization (e.g., Hubbs and Lagler 1958; Minckley and Deacon 1968; Minckley 1973). The red shiner is very aggressive and where introduced may dilute the gene pools of native Cyprinella via hybridization (Mayden 1989). The red shiner is probably hybridizing with the blacktail shiner C. venusta in Alabama (Mettee et al. 1996). This species has also affected the distribution and abundance of native fishes in areas in the West where it has been introduced (Holden and Stalnaker 1975b; Moyle 1976a; Deacon 1988; U.S. Fish and Wildlife Service 1990a, 1995).

Rio Grande cichlid Cichlasoma cyanoguttatum

The Rio Grande cichlid is native to northeastern Mexico and southern Texas.  It is the only cichlid species native the United States.

In addition to being established in a few areas of Florida, the species was most recently found to be well established in the Lake Pontchartrain area. A single specimen was collected in 1996 and several more in 1997 (R. Cashner, pers. comm.). Since then it has become very common in the area and is spreading.

Paradisefish Macropodus opercularis

This Asian air-breathing species of gourami is popular in the aquarium trade.  It has been collected at least twice in Florida and is rumored to have been reproducing in the Everglades circa 1940.  Several specimens were collected from a marsh in Orleans Parish, Louisiana, in 1997.  The status of this species in Louisiana is uncertain. Biologists should be on the look-out for this species in that area.

Bighead carp Hypophthalmichthys nobilis
Silver carp H. molitrix

These two species of Asian carp were originally imported to control algal blooms in aquaculture facilities.  Since then they have become established in the wild through stocking and escapes from aquaculture facilities.  These species are becoming increasingly more common in the Mississippi River.  There is concern that they may compete with other phytoplankton-feeding fish such as the paddlefish Polyodon spathula and native larval fishes.

Literature Cited

Bailey, R.M., and C. Gans. 1998. Two new synbranchid fishes, Monopterus roseni from peninsular India and M. desilvai from Sri Lanka. Occasional Papers of the Museum of Zoology, University of Michigan 726:1-18.

Day, F. 1958. The fishes of India; being a natural history of the fishes known to inhabit the seas and fresh waters of India, Burma, and Ceylon, volume I. William Dawson and Sons Ltd., London, England.

Devivo, J.C., and B.J. Freeman. 1995. Impact of introduced Cyprinella lutrensis on stream fish assemblages in Georgia. Abstracts of the 56th Annual Meeting of the Association of Southeastern Biologists. Association of Southeastern Biologists Bulletin 42(2):129.

Fuller, P.L., L.G. Nico and J.D. Williams. 1999.  Nonindigenous Fishes Introduced into Inland Waters of the United States. Special Publication 27.  American Fisheries Society, Bethesda, MD. 613 pp.

Hubbs, C. L., and K. F. Lagler. 1958. Fishes of the Great Lakes Region. University of Michigan Press, Ann Arbor.

Merrick, J. R., and G. E. Schmida. 1984. Australian freshwater fishes: biology and management. Griffin Press, Netley, South Australia.

Minckley, W. L. 1973. Fishes of Arizona. Arizona Fish and Game Department. Sims Printing Company, Inc., Phoenix, AZ.

Nico, L. G., S. J. Walsh, and R. H. Robins. 1996. An introduced population of the South American callichthyid catfish Hoplosternum littorale in the Indian River Lagoon system, Florida. Florida Scientist 59(3):189-200.

Reis, R. E. 1997. Revision of the Neotropical catfish genus Hoplosternum (Ostariophysi: Siluriformes: Callichthyidae), with the description of two new genera and three new species. Ichthyological Exploration of Freshwaters 7(4):299-326.

Starnes, W.C., R.T. Bryant, and G.C. Greer. 1998.  Perilous experiment: the Asian rice eel in Georgia. Urban Wildlife (Georgia Wildlife) 7(1):60-70.

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