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Potentially Misidentified Species:
S. melanotheron is similar in appearance to other tilapine fish
species (including the genera Tilapia, Oreochromis, Cichlosoma and
Sarotherodon) and to many cichlids in general. Several of these species
can be found as co-occurring non-natives in locations where S.
melanotheron has become established. The presence and location of the
dark coloration on or around the chin aid in species identification.
II. HABITAT AND DISTRIBUTION
Regional Occurrence:
S. melanotheron is a demersal (bottom-associated) species
inhabiting fresh to brackish water where it occurs. It is a
tropical west African native occurring from Senegal to Zaire and
southern Cameroon (Trewevas 1983, Robbins et al. 1991). The
species is common in quiet muddy backwater habitats where aquatic
vegetation is abundant (Jennings and Williams 1992). Outside of
its native range, blackchin tilapia have been introduced to several
countries across Asia, North America, and Europe (Wohlfarth and
Hulata 1983).
Florida is the only state in the Gulf region in which S.
melanotheron has become established (Courteney et al. 1991,
Jennings and Williams 1992). In Florida, blackchin tilapia have
been collected on the Gulf coast from freshwater and brackish
habitats in Hillsborough County southward to Manatee County
including the eastern shore of Tampa Bay (Courtenay et al. 1984).
Specimens have also been collected from Alachua, Palm Beach, and
Pinellas counties.
The species is also established on Florida's east coast within the
IRL watershed (see below).
IRL Distribution:
Within the IRL watershed, blackchin tilapia have been collected in
Brevard, Indian River and Palm Beach counties. It is well
established in Brevard County and may be established in the other
IRL counties as well. S. melanotheron can now be found from Cocoa Beach
in Brevard County south to around Vero Beach in Indian River
County. In Brevard County, blackchin tilapia occupy the estuary
proper as well as adjacent drainage canal networks and mosquito
impoundment marshes (Dial and Wainright 1983, Courtenay et al.
1984, Jennings and Williams 1992).
Northward expansion beyond the IRL is likely limited by winter
water temperatures, although southward expansion appears not to be
temperature limited (Jennings 1991, Jennings and Williams 1992).
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Blackchin tilapia have been reported to reach 28 cm standard length (SL)
(Olaosebikan and Raji 1998). In Florida, they commonly attain 22
cm standard length and 24 cm SL is possible (Finucane and Rinckey
1964, Hensley and Courtenay 1980).
Abundance:
This exotic species can be extremely abundant on local scales.
Courtenay et al. (1974) suggested that the S. melanotheron
population in Lithia Springs, Florida, accounted for 90% of the
total fish biomass in that system. The authors also speculated
that similarly large S. melanotheron populations were established in
the Tampa Bay area.
Within a seasonally impounded IRL mangrove ecosystem, Faunce (2000,
personal communication) reported that blackchin tilapia were the
dominant fish species by weight. Dial and Wainright (1983) report
abundance of the species in the IRL in estuarine shallows and
within the extensive drainage canal network.
Reproduction:
Over its natural range, spawning occurs year-round, but activity
declines in periods of heavy rainfall (Trewevas 1983).
In Florida, spawning has been observed form March to November. In
the IRL region, Faunce (2000) observed spawning from April to
October but gonadosomatic indices revealed that spawning activity
peaked in April and May.
Trewevas (1983) reports the formation of stable breeding pairs with
females initiating courtship and nest construction and males
mouth-brooding the eggs and young. Females will aggressively
defend nest sites while males are mouth-brooding (Jennings and
Williams 1992).
Trewevas (1983) also indicated that S. melanotheron can achieve
sexual maturity at a very small body size, a trait of adaptive
advantage for an opportunistic invasive species.
Embryology:
Females produce a clutch of approximately 50 orange eggs that vary
from 1.5-4.5 mm in diameter depending on the size of the female.
Incubation within the buccal cavity ("mouth brooding") by the male
ranges from 6-22 days, averaging about 14 days (Finucane and
Rinckey 1964, Trewevas 1983).
IV. PHYSICAL TOLERANCES
Temperature:
S. melanotheron is a tropical species whose native range in the
northern hemisphere extends from the equator to 18ºN (FishBase)
and winter temperature extremes are likely the factor most
limiting factor northward range expansion (Shafland and Pestrak
1982, Jennings 1991, Jennings and Williams 1992).
A lethal low temperature of 10.3ºC has been established by
Shafland and Pestrak (1982) who suggested that Daytona Beach
represented the probable northern limit of the expanding range of
this species in Florida. Other reports indicate Florida
blackchin tilapia populations can survive seasonal low
temperatures of around 9ºC (Springer and Finucane 1963,
Crittenden in Finucane and Rickley 1964).
In the late 1980s in the IRL near Merritt Island, blackchin
tilapia suffered a widespread thermal fishkill when winter air
temperatures fell to 0ºC (Snodgrass 1989).
Finucane and Rickley (1964), suggested spawning would cease below
25ºC for spawning to occur while Schreitmuller in Trewevas (1983)
reported failure of breeding pairs to successfully rear young at
temperatures below 23ºC.
Salinity:
Blackchin tilapia are broadly euryhaline, primarily inhabiting
estuarine habitats such as mangrove marshes, and travel freely
between fresh and saltwater environments (Trewevas 1983, Shafland
1996). They frequent the saline lower reaches of streams and are
also tolerant of hypersaline conditions that may arise in enclosed
lagoons and impounded marshes (Page and Burr 1991).
Although the IRL watershed canals and ditches that are home to many
blackchin tilapia typically do not exceed 10 ppt, individuals have
survived experimental exposure to salinities that are ten times
that level (Jennings and Williams 1992). This fish is capable of
spawning both in full seawater and in pure freshwater (Shaw and
Aronson in Trewevas 1983, Jennings and Williams 1992).
Within the Brevard County portions of the IRL watershed, S.
melanotheron persists in freshwater as well as at salinities of up
to 30 ppt (Dial and Wainright 1983, Snodgrass 1989).
V. COMMUNITY ECOLOGY
Trophic Mode:
Blackchin tilapia exhibit an ontogenic dietary shift, switching
from a more carnivorous habit as juveniles to an adult diet that
focuses mainly on detritus, algae, periphyton and the organisms and
material inhabiting or fouling submerged hard surfaces (Hensley and Courtenay
1980, Diouf 1996). The many small teeth, with their spoon-shaped
crowns, are well-suited to such a diet (Trewevas 1983).
Associated Species:
Associations with other species within the non-native range of
the blackchin tilapia are likely to be competitive in nature,
with food and space being the disputed resources. See below for
more information.
VI. INVASION INFORMATION
Invasion History:
The blackchin tilapia was the first of at least six species of
tilapia that have been released into Florida environments (Shafland
1996). The species was originally imported into the United States
to be raised and sold for the aquarium trade (Axelrod and Schultz
1955). Initial release to the natural environment was most likely
an accidental escape from a west coast fish farm in the mid-1950s.
Introduction of blackchin tilapia to Florida waters initially
occurred near Tampa Bay in the 1950s, through release associated
with the aquarium trade (Springer and Finucane 1963, Courtenay and
Robins 1973, Hensley and Courtenay 1980, Jennings and Williams 1992). The
first records confirming collection of this species from the wild on
the west coast of Florida date to 1959 (Springer and Finucane
1963).
The east coast IRL watershed blackchin tilapia population became
established substantially later; the first reported collection from
the wild dates to 1980 from Satellite Beach in Brevard County (Dial
and Wainright 1983).
The east coast population may also derive from aquarium releases or
aquaculture escapes, although there is some speculation that it
resulted from an intentional introduction by fishermen (Dial and
Wainright 1983, Jennings and Williams 1992). One additional IRL
introduction pathway has been proposed that points to escape of this
species from an ornamental pond located at the Satellite Beach Civic
Center where it was used to control the growth of algae (Dial and
Wainright 1983). Regardless of the actual mechanism, authors have
suggested Satellite Beach as the likely epicenter for the east coast
S. melanotheron introduction (Dial and Wainright 1983, Jennings and
Williams 1992).
Thermal tolerance limits may restrict northward expansion of the
Florida range of blackchin tilapia, but there appears to be no
similar mechanism limiting southward range expansion (Snodgrass
1989, Jennings and Williams 1992).
Potential to Compete With Natives:
Large populations of S. melanotheron likely compete with
native fish populations for resources. Courtenay et al. (1974)
provide circumstantial evidence, noting a malnourished and diseased
appearance in largemouth bass and bluegills co-occurring with
non-native blackchin tilapia in a Florida freshwater spring. In
addition to dietary items, blackchin tilapia may compete with other
species for breeding and nesting space, as is typical for cichlids.
Direct predation of S. melanotheron on co-occurring native species
may be less important than competitive interactions. Given their
adaptability and euryhaline habit, however, the species
nevertheless has the ability to dominate systems it invades
potentially resulting in biodiversity reduction (Dial and Wainright
1983). FishBase rates the resilience of S. melanotheron as "medium"
based on an estimated minimum population doubling time of 1.4 - 4.4
years.
Established populations of blackchin tilapia have been associated
with a reduction of aquatic vegetation due to overgrazing
(Courtenay et al. 1974).
Possible Economic Consequences of Invasion:
Blackchin tilapia have been exploited as a food resource in their
native range, and have been utilized as an aquaculture and
non-native fishery species elsewhere as well. Early records of
commercial utilization in Florida date from 1959, when the species
was marketed under the name "African sunfish" (Springer and
Finucane 1963). S. melanotheron taken from Florida waters are
included as commercial fishery landings, but no estimate on the
value of this fishery component has been assessed.
No studies have been reported that fully evaluate the economic
impacts this exotic fish has had on freshwater, marine, and
estuarine systems in Florida.
VII.
REFERENCES
Axelrod H.R. and L.P. Schultz. 1955. Handbook of tropical aquarium fishes.
McGraw-Hill Book Co., New York. 718 p.
Courtenay W.R., Jr., and C.R. Robins. 1973. Exotic aquatic organisms in Florida
with emphasis on fishes: A review and recommendations. Transactions of the
American Fisheries Society 102:1-12.
Courtenay W.R., Jr., Sahlman H.F., Miley, II W. W. and D. J. Herrema. 1974.
Exotic fishes in fresh and brackish waters of Florida. Biological Conservation
6:292-302.
Courtenay W.R., Jr., Hensley D.A., Taylor J.N. and J.A. McCann. 1984.
Distribution of exotic fishes in the continental United States. Pages 41-77 in
Courtenay W.R., Jr., and J.R. Stauffer, Jr. (eds.). Distribution, biology and
management of exotic fishes. Johns Hopkins University Press, Baltimore, MD.
Courtenay W.R., Jr., Jennings D.P., and J.D. Williams. 1991. Appendix 2, exotic
fishes. Pp 97-107 in: Robins C.R., Bailey R.M., Bond C.E., Brokker J.R.,
Lachner E.A, Lea R.N., and W.B. Scott (eds.). Common and scientific names of
fishes from the U.S. and Canada. Special Publication 20, American Fisheries
Society, Bethesda, MD.
Courtenay W.R., Jr., Sahlman H.F., Miley W.W., and D.J. Herrema. 1974. Exotic
fishes in fresh and brackish waters of Florida. Biological Conservation
6:292-302.
Dial R.S. and S.C. Wainright. 1983. New distributional records for non-native
fishes in Florida. Florida Scientist 46:8-15.
Diouf P.S.1996. Les peuplements de poissons des milieux estuariens de l'Afrique
de l'Ouest: L'exemple de l'estuaire hyperhalin du Sine-Saloum.. Universite de
Montpellier II. Theses et Documents Microfiches No.156. ORSTOM, Paris. 267 p.
Faunce C.H. 2000. Reproduction of blackchin tilapia, Sarotherodon
melanotheron, within an impounded mangrove ecosystem in east-central
Florida. Environ. Biol. Fishes 57:353-361.
Finucane J.H., and G.R. Rinckey. 1964. A study of the African cichlid,
Tilapia heudeloti Drumeril, in Tampa Bay, Florida. Proceedings of the
Annual Conference of the Southeastern Association of Game and Fish
Commissioners 18:259-269.
FishBase. 2007. Froese R. and D. Pauly (Eds). World Wide Web electronic
publication.
http://www.fishbase.org(version 02/2007).
Hensley D.A. and W.R. Courtenay, Jr. 1980. Tilapia melanotheron
(Ruppell) Blackchin Tilapia. In: Lee D.S., Gilbert C.R., Hocutt C.H., Jenkins
R.E., McAllister D.E. and J.R Stauffer, Jr. Atlas Of North American Freshwater
Fishes. North Carolina State Museum Of Natural History, Special Publication
1980-12 Of The North Carolina Biological Survey.
Jennings D.P. 1991. Behavioral aspects of cold tolerance of blackchin tilapia,
Sarotherodon melanotheron (Pisces, Cichlidae) at different salinities.
Environmental Biology of Fishes 31:185-195.
Jennings, D.P. and J.D. Williams. 1992. Factors influencing the distribution of
blackchin Tilapia Sarotherodon melanotheron (Osteichthyes: Cichlidae) in
the Indian River system, Florida. Northeast Gulf Science 12:111-117.
Olaosebikan B.D. and A. Raji. 1998. Field guide to Nigerian freshwater fishes..
Federal College of Freshwater Fisheries Technology, New Bussa, Nigeria.106 p.
Page L.M. and B.M. Burr. 1991. A field guide to freshwater fishes of North
America north of Mexico. Houghton Mifflin Company, Boston. 432 p.
Robins, C.R., Bailey R.M., Bond C.E., Brooker J.R., Lachner E.A., Lea R.N. and
W.B. Scott, 1991. World fishes important to North Americans. Exclusive of
species from the continental waters of the United States and Canada. Am. Fish.
Soc. Spec. Publ. 21. 243 p.
Shafland P.L. 1996. Exotic Fishes of Florida-1994. Reviews in Fisheries Science
4:101-122.
Shafland P.L. and J.M. Pestrak. 1982. Lower lethal temperatures for fourteen
non-native fishes in Florida. Environmental Biology of Fishes 7:139-156.
Snodgrass J.W. 1991. Winter kills of Tilapia melanotheron in coastal
southeast Florida, 1989. Florida Scientist 54:85-86.
Springer V.G., and J.H. Finucane. 1963. The African cichlid, Tilapia
heudeloti Dumeril, in the commercial fish catch of Florida. Transactions of
the American Fisheries Society 92:317-318.
Trewevas, E. 1983. Tilapiine Fishes of The Genera Sarotherodon, Oreochromis
and Danakilia. British Museum Of Natural History, Publ. Num. 878.
Comstock Publishing Associates. Ithaca, New York. 583 p.
Wohlfarth, G.W. and G. Hulata. 1983. Applied genetics of tilapias. ICLARM Stud.
Rev. 6. 26 p.
Report by:
J. Masterson, Smithsonian Marine Station
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