Established Nonindigenous Fish Species in
Florida
Oscar (Astronotus ocellatus).
The oscar is native to the Orinoco, Amazon, and La Plata river systems of
South America. This popular aquarium species first appeared in canals in
Miami, Dade County, Florida, in the late 1950s after a deliberate release
from an aquarium fish farm (Courtenay et al. 1974). It is now established in
Broward, Dade, Glades, Hendry (probably), and Palm Beach counties. Although
the original release may have been from a fish farm, the spread of this
species has been aided by anglers who stocked water bodies with the species
to start new populations. The oscar is a popular sport and food fish
throughout southern Florida and is sought by anglers (P. Shafland, Director,
Non-native Fish Research Laboratory, Boca Raton, Florida, personal
communication). Food-habit studies revealed the diet overlap of this species
with native species and predation by this species on native species. The
bulk of the material in the stomachs of 23 oscars was of animal origin and
included insects, fishes, fish scales, amphibians, and some plant material,
mainly unidentified seeds (Hogg 1974).
Peacock Cichlid (Cichla ocellaris). This
species is sometimes called the butterfly peacock and belongs to the genus
Cichla, which contains several species that are not well described.
This creates confusion among professional fishery biologists. Eigenmann and
Allen (1942) lumped several species as synonyms for Cichla ocellaris
and C. temensis (Ogilvie 1966). The native range of the genus
includes the rivers and lakes of the Amazon regions of Brazil and Bolivia,
Peru, Venezuela, and Guyana. Ogilvie (1966a,b) summarized the general
life-history information and the efforts to evaluate several species of
peacock cichlids for introductions into Florida. Four seemingly different
species were imported into Florida from the Orinoco River in Venezuela. All
of the fishes were evaluated for introduction as game. Some isolated ponds
were stocked with them, but none of the fishes survived, probably because of
water temperatures in winter (Paul Shafland, Director, Non-native Fish
Research Laboratory, Boca Raton, Florida, personal communication). All
species were strictly pisciverous and not selective about size or species of
forage fish. In their native range, some species grow to a maximum size of
13.5 kg, whereas other species average 1 to 2 kg. All species were potential
sport fishes.
In the 1980's, fingerlings of Cichla ocellaris
and C. temensis were imported from different geographical areas in
South America (Brazil, Guyana, and Peru) into Florida and cross bred within
species to maximize genetic species specific variability (Shafland 1984).
Additional peacock cichlids, obtained from Texas, that had originally been
obtained from Florida from the earlier stock, were bred with the recent
imports. Resulting young were raised in Boca Raton, Florida. Between 1984
and 1986, Dade County canals were stocked with 20,000 peacock cichlid.
Spawning began at 27 C. Shafland (1984) stated that studies with control
temperatures conclusively revealed the inability of the peacock cichlid to
survive water temperatures less than 15 C. After comparing the temperature
tolerance found in the literature (Swingle 1966; Guest et al. 1979; Guest
and Lyons 1980) with the results of temperature tolerance tests that he had
completed earlier for other tropical fish species (Shafland and Piestrak
1982), Shafland (1984) concluded that peacock cichlid are considerably less
tolerant of low water temperatures than any other currently established
tropical fishes in Florida. Shafland (1984) later stated that the peacock
cichlid, because of its lower lethal temperature tolerance of 15 C, could
only survive in several major drainage canals in the most southern part of
Florida. Temperatures in the North New River Canal near Ft. Lauderdale
normally fall below 15.6 C (Anderson 1975). Water temperatures in winter
during 1982-83 indicated that the species could survive in canals south of
Miami but not in most natural freshwater habitats like the Everglades--not
even during mild winters (Shafland 1984, 1989, 1990). Peacock cichlids
cannot survive salinities that exceed 18 ppt.
The present established range of the peacock
cichlid includes the coastal canals of eastern Dade and Broward counties
within 50 km of the east coast of Florida and north to the Palm
Beach-Broward county line (Morello 1993). The westward spread extends to the
edge of the Everglades Conservation Area, 4.8 to 9.6 km south of the
junction of U.S. Highway 27 and Interstate Highway 75 (Alligator Alley),
where peacock cichlids have been caught by anglers. Although some fishery
biologists are concerned that the peacock cichlid will become established in
the Everglades National Park, Shafland (P. Shafland, Director, Non-native
Fish Research Laboratory, Boca Raton, Florida, personal communication)
believes that the existing range of the species will be reduced to the
coastal canals of Dade County as soon as a colder-than-average winter
occurs. This species is expanding its range because of its own ability to
spread through interconnecting canals, the continued stocking of waters with
the fish by the Game and Freshwater Fish Commission, and unofficial releases
by anglers into favorite fishing areas. No studies have been conducted to
determine the impact on largemouth bass populations that were in the canals
before the introduction of the peacock cichlids.
The peacock cichlid, released in 1984 by the
Florida Game and Freshwater Fish Commission, was the first legally
introduced exotic species into the waters of Florida (Shafland 1993). It has
overwintered and reproduced every year since it was introduced.
Self-sustaining populations now exist in 530 km of canals, where they are
heavily sought after by anglers. Bait and tackle stores are promoting the
taking of the species, and special guide services have developed for this
species (Tucker 1988). In 1989, a 12-month standard creel census revealed
that people fished for this species. The estimated fishing pressure was
31,662 hours on 40 surface hectares of canal (792 h/ha). This provides an
estimated 425,000 hours of recreational fishing year and an estimated annual
economic worth of $1.4 million (Shafland 1993). Only 2 peacock cichlids/day
can be taken, and only one can be more than 43.2 cm in total length. The
current state record is a 3.4 kg fish caught by an angler in April 1992. The
average size caught by anglers is in the range of 0.5-1.0 kg, but fishes as
heavy as 4.5 kg may be taken.
Speckled Pavon (Cichla temensis). This
species is sometimes called the speckled peacock. It was collected from the
Orinoco River, Venezuela, during earlier efforts to determine the
feasibility of introducing it into Florida (Ogilvie 1966a). It grows at a
slower rate and may be less prolific than the peacock cichlid and is still
protected from harvest in Florida (Chapman 1989). In its native waters,
fishes as heavy as 13.6 kg have been taken. This species is not yet listed
as established in Florida.
Black Acara (Cichlasoma bimaculatum). In
earlier literature (Robins et al. 1991), this species was called the port
cichlid (Aequidens portalegrensis). It was a popular aquarium fish
during 1930-1950. Its native range is eastern Venezuela and Trinidad,
Guyana, Surinam, French Guiana, Brazil, Ecuador (possibly), Bolivia,
Paraguay, Uruguay, and northern Argentina (Regan 1905; Fowler 1954;
Ringuelet et al. 1967). It is established in Broward, Collier, Dade, Glades
(probably), Hendry, Monroe, and Palm Beach counties of Florida (Rivas 1965;
Lachner et al. 1970; Kushlan 1972; Courtenay et al. 1974; Hogg 1976a,b). The
first specimens in the open waters of Florida were found in the early 1960's
(Rivas 1965) and probably escaped or were released from aquarium-fish farms
(Courtnay et al. 1984). Survival and rapid rate of spread of this species
can be attributed to several factors. It is a prolific breeder that spawns
every month and guards its young well into the free-swimming stage (Taylor
et al. 1984). Examination of 23 stomachs of this species indicated that
plant material was a dominant food item and included filamentous algae and
vascular plant fiber; stomach contents also included some chironomidae
larvae and fish scales (Hogg 1974). This species has been collected in
several new localities in southern Florida, indicating that it is continuing
to expand its range (W. Loftus, Biologist, Everglades National Park,
National Biological Survey, personal communication).
Midas Cichlid (Cichlasoma citrinellum).
This species is native to the Atlantic slope of Nicaragua, including the
Great Lakes basin south to Costa Rica (Miller 1966). In 1981, an established
population of this species was discovered in the Black Creek Canal in
southeastern Dade County, Florida (Anderson et al. 1984). The population
extended approximately 10.5 km westward from the salinity structure. A pair
of midas cichlids with young were seen in the C-102 canal in June 1982. An
analysis of the contents of the intestines and stomachs of 16 specimens
revealed plecypods, detritus, gastopods, and plant material. Barlow (1976)
reported that midas cichlids eat young fishes including their own and shift
to a more piscivorous diet as they grow larger. Anderson et al. (1984) found
its lower lethal temperature was 11 C and predicted that this limits the
species' distribution to south of a line connecting Tampa and Melbourne. The
source of this i ntroduction is unknown, but it is generally believed that
the fish was released from one of the fish farms in the area. Anderson et
al. (1984) concluded that any harm from this species would be on fishes that
already suffer from introductions of other nonindigenous species. Recent
observations of this species indicated that it has persisted where it was
established but does not seem to be expanding its range beyond extreme
southern Florida.
Firemouth Cichlid (Cichlasoma meeki). The
native distribution of this popular aquarium fish species is the Atlantic
Slope drainages of South America from the Rio Tonala in Veracruz and
Tabasco, Mexico, to southern Belize, including the Yucatan Peninsula and the
upper Usumacinta basin in Guatemala (Courtenay et al. 1980).
This species shows stress when water temperatures
drop below 17.9 C and dies at 10.3 C (Shafland and Pestrak 1983). Barlow
(1974) classified this species as a substrate sifter, whereas Hogg (1976a)
reported that it fed on nonfilamentous algae, filamentous chlorophyta,
molluscan shell fragments, vascular plant fiber, fish eggs, and insect
parts. Larger fishes tend to feed less on plant material.
Courtenay et al. (1986) discussed the early
distribution in Dade and Palm Beach counties, Florida. It is established in
vicinities of aquarium fish farms in the Tamiami and Snapper creek canals in
Dade County. Page and Burr (1991) reported the species as established in
Dade County, Florida. In 1993, personnel of the National Biological Survey
(National Fisheries Research Center-Gainesville, Florida, personal
communication) found the firemouth cichlid established in several small
mosquito drainage ditches on Big Pine Key, Florida.
Rio Grande Cichlid (Cichlasoma cyanoguttatum).
This species--sometimes called the Rio Grande perch or Texas cichlid--is
native to southern Texas, the lower Rio Grande River and its lower
tributaries, and southward into Mexico. It was probably first introduced
into Florida from Texas stock in 1941 by a private individual (Courtenay et
al. 1974). It was established in an abandoned phosphate pit near Mulberry,
Polk County, where it was reported as numerous, in Dade County southwest of
Miami, and in Hillsbough County. Some of the releases or escaped individuals
were from fish farms. This species is locally established; its divided
populations have not expanded their ranges.
Rio Grande cichlids show stress when the water
temperatures drop to 18.2 C and die at 5 C (Shafland and Pestrak 1982).
Darnell (1962) found that the species is omnivorous but feeds mainly on
vascular plant matter, filamentous fungi and algae, insect larvae,
caterpillars, beetles, water mites, cladocera, and protozoans. Other
researchers also found fish eggs and scales in stomach contents (Buchan
1971).
Jack Dempsey (Cichlasoma octofasciatum).
This popular aquarium fish is native to the Atlantic Slope drainages from
the Rio Chachalacas basin, Veracruz, Mexico, to the Rio Ulua basin in
Honduras, including the Yucatan Peninsula (Miller 1966). It is established
in four Florida counties: in ditches on the University of Florida campus,
Gainesville, Alachua County (Shafland 1982; Courtenay et al. 1986; Jennings
1986); in canals near the Satellite Beach Civic Center and in other canals
from Satellite Beach to Canova Beach, Brevard County (Dial and Wainright
1983); in Black Creek and Snapper creek canals, Dade County (Courtenay et
al. 1974; Hogg 1976a,b); and in a roadside ditch in Ruskin, Hillsborough
County (Courtenay et al. 1974). An established population of this fish was
eradicated from a rockpit in Levy County by the Florida Game and Fresh Water
Fish Commission (Levine et al. 1979). Another population was established in
a canal near an aquarium-fish farm west of Lantana in Palm Beach County
(Courtenay et al. 1974) but seems to have died out. This species has been
collected near Micco, Brevard County, but does not seem to be established
there (Courtenay et al. 1986). This species can survive a salinity of 2-8
ppt. Populations in Dade and Hillsborough counties seem to be escaped
individuals or releases from aquarium-fish farms; those in Alachua and
Brevard counties probably started with released aquarium fishes. A
population of this species, which was studied by Jennings (1986), is still
established in Gainesville, Alacuha County, Florida. Food-habit studies
(ref) indicated that it is omnivorous and feeds opportunistically on
invertebrates, insects, fishes, and vegetation. Hogg (1976a) found its
stomach contained filamentous algae, crayfish exoskeletons, mollusk shell
fragments, and various unidentified material. Levine et al. (1979) found a
predominance of animal matter in its diet.
Temperature tolerance tests indicated that the
lower lethal temperature for this species was 8 C (Shafland and Pestrak
1982). Nevertheless, Jennings (1986) collected it from a small creek
(0.5-4.0-m width and 6-20-cm depth) in Gainesville, Florida, where it was
able to survive an evening air temperature of -2.8 C. The water source was
from an underground drainage system that produced an initial water
temperature of about 25 C. Seemingly small heat sinks, such as existed in
the above case, are sufficient for overwintering by cold-sensitive
populations much farther north than anticipated. This species has the
reputation of being a very aggressive fish. Local populations continue to
exist but do no seem to be expanding. Populations started with escaped
individuals from fish farms or with released aquariums fishes. This species
is considered locally established.
Mayan Cichlid (Cichlasoma urophthalmus).
The native range of this species includes the Atlantic Slope from the Rio
Coatzacoalcos basin in Veracruz, Mexico, south to Nicaragua and the Yucatan
Peninsula, Cozumel, and to Isla Mujeres (Miller 1966).
Specimens of this species were first collected from
Florida's open waters in January 1983 in Snook Creek, a mangrove-lined,
highly hyaline tributary of Joe Bay in the northeastern Florida Bay,
Everglades National Park (Loftus 1987). Later in the year, Loftus collected
more specimens from the Anhinga Trail ponds in the park. Both sites were in
Taylor's Slough. Repeated visits revealed spawning by this species in both
areas (Loftus 1987). This euryhaline cichlid is considered to be established
by Loftus (1987) because it has survived adverse environmental conditions
such as cold spells, droughts, and floods for 3 years. The source of this
introduction is unknown, but it was probably a release into the two disjunct
areas by an aquarium hobbyist (Loftus and Kushlan 1987; Loftus 1989). The
Mayan cichlid has continued to expand its range and has been taken in
several new locations in the Everglades (W. Loftus, Biologist, Everglades
National Park, National Biological Survey, personal communication). Stomach
contents of eight fishes from Snook Creek consisted of Cerithium,
other snails, and Chara.
Convict Cichlid (Cichlasoma nigrofasciatum).
The convict cichlid is native to the Pacific Slope drainages from Guatemala
to Costa Rica and to the Atlantic Slope drainage of Costa Rica (Miller
1966). It has been reported as established in Nevada, Arizona, and Florida
(Courtenay et al. 1986), however, the population in Florida, reported by
Rivas (1965) in a rockpit in northwest Miami, Dade County, has not been
observed in recent years (Courtenay et al. 1986). This species is no longer
considered as established in Florida.
Yellowbelly Cichlid (Cichlasoma salvini).
This cichlid is native to southern Mexico, Guatemala, Yucatan, and Honduras
and from the Atlantic drainage of the Rio Papaloapam, Veracrux, Mexico, to
the Sulphur River near Puerto Barrios, Guatemala. This species is considered
a snappish and quarrelsome species in aquaria, and, although it is a very
attractive fish, it is not a popular aquarium species. It can survive in
water temperatures of slightly less than 20 C (Sterba 1966). A
well-established, reproducing population of this species was found in a
borrow pit in an abandoned amusement park in Dania, Broward County, in March
1980. Established C. meeki were also found in the same borrow pit.
Because the yellowbelly cichlid population was able to survive unusual and
extremely cold temperatures in February 1981, it was eradicated by the
Florida Game and Fresh Water Fish Commission later that year. However, in
1992 and 1993, the yellowbelly cichlid was found in a canal in Davie,
Broward County, by personnel of the National Biological Survey (National
Fisheries Research Center-Gainesville, Florida, personal communication). The
presence of different size classes suggested multiple spawnings. The species
is considered locally established in Florida.
Redstriped Eartheater (Geophagus surinamensis).
The native range of this species includes the Guianas and the Amazon river
basins of Bolivia, Brazil, Colombia, and Peru (Gosse 1975). In 1982, a
reproducing population of this species was found by personnel of the
Non-Native Fish Research Laboratory, Florida Game and Fresh Water Fish
Commission, in the Snapper Creek Canal, Dade County, Florida (Metzger and
Shafland 1984). Its presence there may be the result of escaped individuals
from a fish farm or from a dumped aquarium. As other locally established
populations of cichlids in southern Florida, the redstriped eartheater has
the potential to expand its range. It was recently collected by National
Biological Survey personnel (National Fisheries Research Center-Gainesville,
Florida, personal communication) from the Snapper Creek Canal in the same
general area where the first specimens were collected. Because the
population shows no signs of spreading, it is considered locally
established. This popular aquarium fish (Axelrod et al. 1980) grows to a
maximum total length of 30 cm (Puyo 1949) and is a bottom feeder.
African Jewelfish (Hemichromis bimaculatus;
now identified as H. letourneauxi by Smith-Vaniz). This species is
native to rivers and lakes throughout western Africa, in the Chad Basin, in
the Nile River, and south to the Congo River (Daget and Iltis 1965). In Dade
County, Florida, it is established in the Hialeah Canal and in connecting
canals to the west and south of the Miami International Airport and in the
Comfort Canal, the channelized South Fork of the Miami River (Rivas 1965;
Courtenay and Robins 1973; Courtenay et al. 1974; Hogg 1976a,b). Courtenay
et al. (1984) reported its probable establishment in a canal east of Goulds,
Florida, and in the Snapper Creek, north of the Tamiami Canal. It has been
collected in a canal near an aquarium-fish farm near Micco, Brevard County,
Florida, but there is no evidence of its establishment. This species seems
to be increasing its range recently because it has been collected in several
new localities (Bill Loftus, Biologist, Everglades National Park, National
Biology Survey, personal communication).
The sources for the introduction of this fish in
Dade County are unknown. Its distribution is largely centered in canals
around the Miami International Airport, which is a major port of entry for
aquarium fishes. Possibly, the jewelfish was released near the airport or
from aquarium-fish farms northward along the Hialeah Canal.
Examinations of 26 stomachs of the African
jewelfish revealed filamentous algae, its own young, assorted insects parts,
and predominantly plant material (Hogg 1976a).
Blue Tilapia (Tilapia aurea =
Oreochromis aureus). This species is native to the Senegal River, the
middle Niger River as far south as Bussa (not recorded from the lower Niger
or from the Volta River), Lake Chad, pools and lagoons of the lower Chari
and Logone rivers, the lower Nile from near Cairo to the Delta lakes (but
seemingly only in freshwater), the Jordan River system, the Na'aman and
Yarkon rivers in Israel, and the Asraq marshes and hot pools at Ein Fashkha,
Jordan (Trewavas 1966).
Sources and reasons for the introduction of this
species into the United States and the establishment of wild populations are
varied and in some cases only suggested. Shelton and Smitherman (1984)
summarized the suitability of this species for aquaculture. Introductions in
Alabama were made by the Auburn University for research (Smith-Vaniz 1968).
To determine the general biology of the species, McBay (1962) conducted
laboratory studies at the Auburn University from April 1959 to May 1960 and
misidentified the fish as Tilapia nilotica. This study included
investigations of spawning behavior and early life history, food habits, and
lower lethal temperature. The species was introduced into Florida initially
by the Florida Game and Fresh Water Fish Commission for research (mostly
biological control) and subsequently by individuals (Crittenden 1962; Buntz
and Manooch 1969a; Courtenay and Robins 1973, 1975; Courtenay et al. 1974;
Harris 1978).
In 1961, 3,000 Nile tilapia (Tilapia nilotica),
later correctly identified as Tilapia aurea (Smith-Vaniz 1968),
were imported into Florida by the Florida Game and Freshwater Fish
Commission for experimental studies. The purpose was to determine the fish's
use as a biological control agent of nuisance aquatic plants and as a sport
fish (Crittenden 1965). Phosphate pits at the Pleasant Grove Research
Station near Tampa were stocked (Ware and Fish 1971; Ware 1973). The species
proved to be a failure as a control agent and as a sport fish; however,
public relation had already promoted it as a superfish. Before the study
could be completed and the results published, the public gained access to
the fish and began spreading it throughout the state. The species may have
also unofficially been given to friends for private ponds. By 1964, Barkuloo
(1964) strongly recommended that this species not be introduced into
Florida's freshwater because experimental studies revealed it provided
little recreation, could survive Florida winters, could become very
abundant, and probably could interfere with the native forage base in some
water bodies.
The spread of the blue tilapia has been rapid.
During a routine survey in 1966, reproducing tilapia were found in Lake
Morton, Polk County (Ware 1973). Eradication was immediately started. The
estimated standing crop in the lake was 163 kg/ha; and blue tilapia were the
second-most abundant species in the lake. The size distribution revealed
three year classes, indicating that the species had reached that population
level in only 3 years. When a reproducing population was found in Lake
Parker, an 810 ha lake, which is in the headwaters of the Peace River
watershed, all efforts to stop its spread were abandoned (Ware 1973). In
1968-1969, only 2 years after the introduction, blue tilapia comprised 5% of
the composition by weight in samples from Lake Parker (Horel 1969). By 1972,
this fiqure jumped to 68% of the composition by weight (Babcock 1974). The
tilapia population remained at a high level until an apparent die-off from
cold weather. Some tilapia survived or the lake was again stocked with them
because they are still present there. The existence of a power plant on the
lake almost guarantees survival of the species in even cold years.
In 1976, blue tilapia were first collected in Lake
Tohopekaliga, Florida. During 1979-1981, the juvenile tilapia population
increased by approximately 500%/year (Hulon and Williams 1983). The lake is
eutrophic because it receives in excess of 91 million liters/day of
secondarily treated sewage effluent from the greater Orlando metropolitan
area.
The rapid spread of the tilapia across the state
can be attributed to its releases by humans, flooding, natural migrations,
and piscivorous birds (Foote 1977). The existence of highly eutrophic water
bodies also assisted in its survival and spread. Establishment of this
species may harm some Florida ecosystems; however, it created a commercial
fishery in some lakes that would otherwise have been ecosystems with low
yields (Langford et al. 1978). Wattendorf et al. (1980) studied the
interspecific interactions between blue tilapia and other native fishes in
Florida.
In Florida this species is now established in 18
counties: Alachua, Brevard, Dade, DeSoto, Hardee, Hernando, Hillsborough,
Lake, Manatee, Marion, Orange, Osceola, Palm Beach, Pinellas, Polk,
Sarasota, Seminole, and Volusia. Foote (1977) recorded the species from
Broward, Charlotte, Glades, and Pasco counties, but we know of no specimens
from these counties. This species is also reproducing in the saline waters
of Tampa Bay.
Zale (1984) summarized the literature on the lower
lethal-temperature tolerance of the blue tilapia. It varied from 5 to 12 C,
depending on the circumstances or the type of test (Yashou 1960; McBay 1962;
Crittenden 1965; Germany and Noble 1978; Lee 1979; Shafland and Prestrak
1982). The fishes exhibited some form of stress as the temperature dropped
below 12 C and died at 5 C. If the species is preconditioned for warmer
temperatures, the fish is already stressed, the period of decreasing
temperatures is prolonged, or the drop in temperature is rapid, death can
occur at higher than 5 C. In the wild, the northern expansion of the blue
tilapia population in the United States is limited to the southern part of
the southern tier of states unless a source of heated water such as a power
plant or a warmwater spring is available. During cold weather, all culture
of this species in the colder climates depends on a heated water source or
overwintering of the species indoors. Zale (1987) discussed the behavior of
the blue tilapia that seasonally migrate into stenothermal spring runs in
north-central Florida to escape colder waters of the St. Johns River,
Florida, in winter. The species can probably survive in larger water bodies
in Florida without seeking refuge.
The main component of the blue tilapia diet is
phytoplankton, a small percentage of which is insects such as chironomid
larvae (McBay 1962; Manooch 1972; Stickney 1976). McBay (1962) found that
the smaller, less-than-50-mm tilapia used zooplankton such as rotifers,
copepodes, cladocerns, and ostracodes (Foote 1977).
The impact of blue tilapia on receiving ecosystems
can vary by ecosystem and by the relative abundance of the fishes to native
species. In some water bodies, the tilapia population does not explode but
remains in balance with native predators that control it. In fact, in some
water bodies, the tilapia may be an important prey species of native
predators (Shafland and Pestrak 1981). In other water bodies--probably
because native predators were inadequate to control the tilapia, the system
was already stressed, or turbidity or vegetation cover interfered with
predation on the tilapia (Schramm and Zale 1985)--the tilapia population
exploded. Noble et al. (1975) found that, when the tilapia population
reached a high biomass near 1,121 kg/ha, the blue tilapia spatially
displaced native species and interfered with their reproduction. Competition
for spawning sites between native centrarchids and mouth-brooding tilapia in
Florida have repeatedly been cited (Buntz and Manooch 1969a; Babcock and
Chapman 1973; Courtenay et al. 1974; Harris 1978 and Zale 1984). Noble et
al. (1975) concluded that if blue tilapia could be managed at an
intermediate level where they did not interfere with the reproduction of
largemouth bass, they would not only be a valuable forage for bass but could
provide a sizeable, harvestable food fish. A large population of blue
tilapia in a body of water can suppress recruitment in largemouth bass.
Swingle (1956), Chew (1973), and Shafland and Pestrak (1983) discussed the
possible mechanisms: behavioral interactions (harassment) during
reproduction; predation by normally non-piscivorous species because of
crowding; and competition for food between basses and tilapia young-of-year
or chemical suppressive factors (Swingle 1956; Chew 1973). Blue tilapia
build nests on or close to preferred spawning sites of largemouth bass and
bluegills. Because they usually begin to build nests when largemouth bass
and bluegills spawn, male tilapia may interfere with the spawning of the two
species. Zale (1984) found that male tilapia occupied the spawning beds in
Silver Glenn Springs several months before they were ready to spawn. When
nest building by tilapia is most active in 1-2 m of clear water, the
shoreline looks as if it had been bombed with large 30-cm-wide
depressions--some are as deep as 45 cm. No nests or spawning by native
species is usually evident in or near tilapia nesting areas while the
tilapia are spawning (personal observation). Our recent visits to Silver
Glenn Springs in mid-February 1993 revealed that the tilapia population was
not as large as during the early 1980's (Zale 1984), and many nests were
abandoned. We also observed bow fishing from recreational boats in the clear
water run from the spring. Interviews with hunters in three boats indicated
that this sport was popular in this area and conducted almost year round;
however, it was concentrated in the colder months when the fishes sought
refuge in the warmer water. This hunting effort removed large numbers of
fishes and probably helped to manage the tilapia population. By 10:00 h on
the day of the observations, more than 35 adult fishes with an estimated
weight of more than 2.25 kg had been removed prior to our interview of the
group. Discussions with the hunters indicated that hunting had been slow
that day. No information was available on the total number of annually
removed fishes or the total number of removed fishes on that day.
Like most other tilapia species, the blue tilapia
has a tendency to overpopulate waters where native predators are stressed or
already low in abundance or where turbidity impedes efficient feeding by
predators (Forest Ware, Florida Game and Fresh Water Fish Commission,
Tallahassee personnel commnuication). Highly eutrophic water bodies with
heavy algae blooms tend to become overpopulated with tilapia. Shafland and
Pestrak (1983) speculated that an abundance of this species in any water
body may also adversely affect the forage base of the community. In Texas
and Florida, increases in densities of blue tilapia in eutrophic water
bodies negatively related to sharp declines in native shad populations (Horel
1969; Babcock and Chapman 1973; Ware 1973; Shafland et al. 1980; Wattendorf
1981, 1982). Food-habitat studies by McBay (1962) revealed overlapping diets
with native species.
Rapid spread and high standing crops of this
species have been reported many times (Buntz and Manooch 1969a; Courtenay
and Robins 1973; Ware 1973; Courtenay et al. 1974). Horel (1969) and Babcock
and Chapman (1973) documented an explosion of the tilapia population in Lake
Parker, Polk County, Florida. Ware (1973) concluded that the abundance of
blue tilapia depends on primary productivity of the water body. High
densities develop in eutrophic waters. Denzer (1966) believes that the
ability of blue tilapia to withstand periods of low dissolved-oxygen
concentrations may allow it to survive and flourish in hyper-eutrophic
systems in which many native species cannot survive.
Overpopulation and stunting of tilapia in Florida
adversely affect spawning of native species (Shafland and Pestrak 1983). In
March 1973, in Lake Effie near the city of Lake Wales, almost the entire
population of tilapia died from water pollution (Chapman and Young 1973).
The dead blue tilapia weighed more than 2,242 kg/ha. Lake Effie receives
waste water from two citrus processing plants, and the water is hyper-eutrophic
and sometimes anoxic. Constant aeration is now required to prevent the lake
from going anoxic. Zale (1984) found indications that the spawning of blue
tilapia in Silver Glenn Springs, which discharges directly into the St.
Johns River, may interfere with the spawning of largemouth bass.
In 1970, blue tilapia were first collected from
Lake Lena near Auburndale in Polk County. From 1978 to 1989, fish
populations were sampled and plankton and water chemistry data were
collected to evaluate changes that took place with establishment and
increase of the tilapia population (P. L. Shafland, Director, Non-native
Fish Research Laboratory, Boca Raton, Florida, personal communication). The
data tentatively showed that some populations of native species were
affected as the tilapia populations expanded. Analysis of the data is
presently underway.
Commercial fishing for tilapia by haul seines is
legal in several Florida lakes (lakes Banana, Cannon, Conine, Effie,
Hancock, Hollingsworth, Howard, Lulu, Parker, and Shipp) with a permit from
the Florida Game and Fresh Water Fish Commission (Langford 1976). The lakes
are shallow and enriched with heavy blue-green algae blooms and muck
bottoms. Banana and Lulu lakes are enriched with inflows of domestic sewage,
and heated water from power plant is discharged into Lake Parker (Langford
et al. 1978). The lakes have highly urbanized shorelines and receive
storm-water drainage. Commercial fishery landing of tilapia from each lake
were made every year during 1972-1977 (Langford et al. 1978). The highest
yield, 1,973.2 kg/ha, was from the 41.2-ha Lake Effie in 1975 (Langford et
al. 1978). Some of the lakes still support a small commercial haul-seine or
castnet fishery.
Sale of tilapia produced in the United States must
compete with foreign imports. From July 1992 to June 1993, tilapia imports
into the United States totaled 8.3 million kg at a value of $14.7 million.
The American Tilapia Association estimated that the 1992 U.S. production
reached 4.08 million kg (Zajicek 1993). The volume and value of imports
reduced profits from tilapia by Florida's aquaculture industry (Florida Game
and Fresh Water Fish Commission, Gainesville, Fl., unpublished records). Two
years ago, fresh, ice packed tilapia fillets sold for approximately
$7.85/kg. In 1993, imported frozen tilapia fillets sold for $1.32-$5.48/kg,
depending on the country of origin (Zajicek 1993). The farm-gate prices for
live tilapia in 1994 are about $2.75 at ethnic Asian markets of Chicago,
Philadelphia, New York, and Atlanta.
A computer list, compiled in 1993 by the Florida
Game and Fresh Water Fish Commission, Tallahassee, Florida, showed that
there were 56 permit holders registered for possessing tilapia. A total of
32 permits allowed the culture or sale of tilapia. Only three producers were
selling tilapia in 1993. In 1991, 16 tilapia growers reported Florida's
tilapia sales totalled $572 thousand. Seventy-seven hectares were used in
production, mostly in private phosphorus pits. The sale of tilapia from
aquaculture operations in Florida is in competition with the capture of wild
tilapia with haul seines and cast nets. Because the records and sales of
cultured and wild tilapia are not reported separately, the size of the catch
of the wild tilapia cannot be determined (R. Freie, State Statistician,
Florida Aquaculture Statistics Service, Orlando, Florida, personal
communication).
The potential of tilapia for aquaculture in the
United States is discussed by Suffern (1980). He summarized that tilapia can
be grown outdoors year round only in the deep south or in areas with a
supply of supplemental industrial, solar, or geothermal heat. In some years,
the fishes survive a mild winter, such as the exceptionally warm winter of
1971-72 in Luverne, Alabama (Habel 1975). In this case, the overwintering of
the fishes resulted in the removal of almost 14.2 metric tons of harvestably
sized tilapia, 15 cm or longer, from this 21.4-ha public fishing lake in
1972-73, showing the capability of this species to increase its biomass in a
short time under favorable conditions.
Nile Tilapia (Tilapia nilotica =
Oreochromis niloticus). The Nile tilapia is native to the Nile River
and to coastal rivers of west-central Africa. It is a relatively large
tilapia that attains a total length of 50 cm. It is superficially like the
blue tilapia, Tilapia aureas. Trewavas (1966) distinguished the
Nile tilapia from the blue tilapia and subsequently (Trewavas 1983)
contrasted the Nile tilapia with other tilapia species. Trewavas (1983) also
recognized four subspecies of Oreochromis niloticus.
The only Florida record of the Nile Tilapia a
locally established population in Lake Seminole, Jackson County. Based on a
report in 1993 from the manager of a fishing camp on Lake Seminole, this
tilapia has been caught in the lake since 1988 or 1990. He provided
photographs and specimens of Nile tilapia taken during 1991-93. Survival of
this species during winter is probably linked to availability of warmwater
discharges from numerous springs in the lake. The pathway of this
introduction is unknown but is probably associated with private aquaculture
in the area.
Spotted Tilapia (Tilapia mariae).
Tilapia mariae is native to coastal lowlands in freshwater from the
middle Ivory Coast to southwestern Ghana and from southeastern Benin to
southwestern Cameroon (Thys van den Audenaerde 1966; Trewavas 1974). In its
native habitat, this species prefers brackish water. It is established in
Dade County and Broward County (Hogg 1974, 1976a,b; Courtenay and Hensley
1979, 1980; W. R. Courtenay Jr., Professor, Florida Atlantic University,
Boca Raton, Florida, personal communication). It has also been reported from
a pond south of Copeland and now occupies much of southern Collier County
(W. R. Courtenay Jr., Professor, Florida Atlantic University, Boca Raton,
Florida, personal communication). A population was established near Micco,
Brevard County, in 1979 but subsequently died out. Continuing its rapid
expansion in southeastern Florida, this species now occurs throughout the
New River Canal system in central Broward County, the Tamiami Canal in
western Dade County, in the Aerojet Canal system in Dade County, and
throughout much of the Everglades National Park (Loftus 1989). Based on
recent collections of National Biological Survey personnel (National
Fisheries Research Center-Gainsville, Florida, personal communication), it
is the most common nonindigenous species in canals in southern Florida. It
has been found below salinity dams in three Dade County canals leading into
Biscayne Bay, and monitoring of movements by this euryhaline species is
underway. Hogg (1974, 1976a,b) suggested that Florida populations originated
with escaped individuals or releases from aquarium-fish farms. Courtenay and
Hensley (1980) suggested a possible purposeful release of this fish near
Miami.
Adults grow to a length of approximately 23 cm. It
is not a mouth brooder but protect its eggs and fry (Courtenay and Hensley
1979b). The species is aggressive toward native and toward other
nonindigenous species. This species could replace many other species because
it is expanding its population. The success of this species is attributed to
its prolific reproduction, spawning during all months of the year, and
guarding of its young into the free-swimming stage (Taylor et al. 1984). The
contents of 58 stomachs of this species contained filamentous algae,
non-filamentous algae, vascular plant fibers, and bryozoa. Plant material
was five times more important than animal material. The smaller individuals
are more omnivorous, but larger individuals were herbivorous. The species
seems to do best in canal systems with steep sides and limited shallow
areas.
Blackchin Tilapia (Tilapia melanotheron =
Sarotherodon melanotheron). This species is native to river-delta
lagoons from middle Liberia to southern Cameroon (Thys van den Audenaerde
1971). It is established in Florida in Hillsborough County from Lithia
Springs to the mouth of the Alafia River, and southward along the eastern
shore of Tampa Bay to Cockroach Bay, Manatee County (Springer and Finucane
1963; Finucane and Rinckey 1964; Buntz and Manooch 1969b; Lachner et al.
1970; Courtenay et al. 1974).
It is also established in Brevard County in canals
near Satellite Beach and in the Indian and Banana rivers from Merritt Island
southward to below Canova Beach, a distance of 27 km (Dial and Wainright
1983). Springer and Finucane (1963) suggested that this species either
escaped or was released from an aquarium-fish farm on the eastern shore of
Tampa Bay. The Brevard County population may have resulted from
aquarium-fish releases into the reflecting pool at the Satellite Beach Civic
Center or by anglers attempting to establish a sport or commercial fishery
on the east coast similar to the one on the west coast of Florida. This
species is now taken in commercial catches by netting in estuarine waters
and by hook and line in freshwater (Dial and Wainright 1983). Finucane and
Rinckey (1964) and Anderson (1981) summarized the results of food-habit
studies that revealed the diet overlap between this species and native
species.
On the east coast of Florida, this species spread
southward to the Jupiter Inlet, Palm Beach County, by August 1990. The
northern limit of its range is the Ponce de Leon Inlet near New Smyrna
Beach, Volusia County (Jennings and Williams 1992). They found the species
in a variety of habitats including canals, drainage ditches, lagoonal areas
at the mouth of creeks and canals, open water areas, and freshwater
tributaries. The species prefers quiet backwaters with aquatic vegetation
and a mucky, organic substrate. There is no recent information of its status
on the west coast of Florida in the Tampa Bay tributaries except that it is
still present in some of the same streams where it was previously found. Its
population is considered to be expanding at least on the east coast of
Florida.
Mozambique Tilapia (Tilapia mossambica =
Oreochromis mossambicus). The native range of this species is the
eastward-flowing rivers of Africa from the lower Zambezi and Shire river
systems in Mozambique southward in coastal drainages to Algoa Bay, South
Africa (Jubb 1967; Thys van den Audenaerde 1968). It is established in
Florida in the saline Banana River near Cocoa Beach, Brevard County (Dial
and Wainright 1983), and throughout Dade County (Courtenay et al. 1984; W.
R. Courtenay Jr., Professor, Florida Atlantic University, Boca Raton,
Florida, personal communication). Dial and Wainright (1983) found this
species in brackish water with salinity as high as 8 ppt in the Satellite
Beach area. Populations in Brevard County seem to have originated from
stocks of aquarium fishes released at Satellite Beach (Courtenay et al.
1974; Dial and Wainright 1983). Most of those in Dade County probably
escaped from aquarium-fish farms. At one locality, their establishment
resulted from an introduction for aquatic plant control by a developer
(Courtenay et al. 1984). The Mozambique tilapia seems to have maintained
populations in canals where it was originally found in Dade County, Florida.
It seemingly has not spread over any appreciable distance in recent years in
southern Florida. No Mozambique tilapia were found during the surveys of
nonindigenous fishes in the Indian River system by Jennings and Williams
(1992).
Lower lethal-temperature tests indicated that this
fish stops feeding at 15.6 C; individuals began to die at 14.4 C, and all
individuala were dead at 8.3 - 9.4 C (Kelly 1955). Kelly (1955) concluded
that this species could not survive winter conditions throughout most of the
Southeast.
Kelly (1955) conducted food studies that revealed
diet overlap of this species with native species. Studies in its native
range of South Africa indicated that young of this species fed mainly on
detritus and neuston in eulittoral pools and in shallow margins along shore.
Adults fed mainly on detritus, periphyton, and insects in shallow water (Bruton
and Boltt 1975). Kelly (1955) reported that the diet of this species was
mainly composed of planktonic forms of plants and animals. Wieland et al.
(1982) compiled a complete biological synopsis on this species.
Hybrid crosses of this species with other tilapia
species have been used in Florida and elsewhere in the United States for
aquaculture (Wieland et al. 1985). Most culture of this species in Florida
is used for brood stock to establish and supply aquaculture facilities in
foreign countries. This species has a tendency toward overpopulating waters
and toward having stunted growth, thus making it a problem in culture and in
the open waters (Wieland et al. 1985). Swingle (1958) discussed the use of
this species for culture in ponds. Most commercially sold tilapia in Florida
are blue tilapia, not Mozambique tilapia.
The Mozambique tilapia was introduced into open
waters as a weed-control agent in Arizona (Minckley 1973) and as control
agents of aquatic plants, mosquitos, and chironomids in California (Knaggs
1977; Legner and Pelsue 1977) and elsewhere in the world. Its ability to
control nuisance aquatic plants is now considered questionable because its
well being seems to depend on the availability of other food. The
destruction of higher plants seems to be the result of the tilapia scraping
the periphyton from the leaves and from the stalks of the plants. In doing
so, the Mozambique tilapia injure the plants enough to control their growth
(Wieland et al. 1985). Released individuals of these species to control
weeds in California created established, overpopulating populations that are
replacing native species, especially in estuaries (Knaggs 1977; Legner et
al. 1980).
Redbelly Tilapia (Tilapia zilli). This
species of tilapia occurs in Africa in the Bandama, Benue, Chari, Ituri,
Niger, Sassandra, Senegal, Ubangi, Uele, Volta rivers; in lakes Albert,
Chad, and George; and in the Near East in the Jordan River (Thys van den
Audenaerde 1968).
In Florida, the species was established in a
rockpit near Perrine, Dade County, but was eradicated by personnel of the
Florida Game and Fresh Water Fish Commission (Courtenay et al. 1984). Prior
to its eradication, it hybridized with introduced spotted tilapia (Taylor et
al. 1986). The redbelly tilapia recently was found in several mosquito
drainage ditches on Big Pine Key, Monroe County, Florida.
Congo Tilapia (Tilapia rendalli). This
species, formerly identified as T. melanopleura, was studied as a
possible biological control agent of aquatic plants at Lake Wales, Polk
County. The studies revealed that it was highly aggressive, potentially
threatening to native vegetation, and capable of causing problematic
management of native fishes and waterfowl; therefore, the research was
terminated and the population destroyed (Courtenay et al. 1974).