Blue Tilapia (Tilapia aurea). This species invaded the coastal waters of Tampa Bay and Boca Ciega Bay near St. Petersburg in southern Pinellas County, Florida, in 1978 (Courtenay and Hensley 1979a). Hensley first learned of the observation or collections of specimens in the Bayboro Harbor area in January and February 1976 and collected some specimens from Salt Creek in 1978. The population in the western Tampa Bay probably entered the bay from Lake Maggiore, St. Petersburg, where blue tilapia had been established for many years. The introduction into Lake Maggiore was probably the result of escape or release from a nearby aquaculture and subsequent migration downstream. The blue tilapia has been nesting in the saline waters of Tampa Bay (Courtenay et al. 1986). Loftus (1986) reported that this species existed in the estuarine waters of the Everglades National Park.
Blackchin Tilapia (Tilapia melanotheron). This species is native from Senegal to Gabon in West Africa. It was imported into the United States by tropical fish dealers and sold as a popular tropical aquarium fish (Axelrod and Schultz 1955). There was some early confusion about the correct identification of this species (probable synonyms include Tilapia macrocephala (Bleeker) and T. heudeloti (Aronson 1949)). The early established populations of Tilapia along the east coast of Tampa Bay probably consisted of only T. melanotheron. The introduction of this species was probably an escape or accidental release from a fish farm in the mid-1950's. The present distribution of this species on the west coast of Florida extends from the Alafia River southward along the east 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).
The blackchin tilapia was first caught in Hillsborough Bay in late summer 1959 in a gillnet set by mullet fishermen between Mangrove Point and the Alafia River (Springer and Finucane 1963). In 1962, one commercial fish dealer sold 1,589 or 2,043 kg of tilapia from the west coast population. The most consistent collecting sites was near Dug Creek that received drainage from a fish farm (Finucane and Rinckey 1964). Springer and Finucane (1963) reported hearing that one tropical fish farm went out of business and dumped its entire fish stock into a local stream (Springer and Finucane 1963). This one action could be responsible for many of the exotic fish species that are established in the Tampa Bay area.
In 1962, regular sampling was initiated in the area as part of the East Gulf Estuarine Program on Tampa Bay (Finucane and Rinckey 1964). An ecological and life history study of the fishes was conducted. At that time, the distribution of the blackchin tilapia extended from the Alafia River to Mangrove Point along the eastern shore of the Upper Tampa and Hillsborough bays. More recent sampling indicated the species migrated up the freshwater streams such as the Alafia River. In this river, it migrated upstream into the headwaters, Lithia Springs, where it and the blue tilapia became a dominant species, replacing many native species (personal observation). Springer and Finucane (1963) stated that this species was well established in the Little Manatee River system in Ruskin.
On the east coast of Florida, the first collection of the blackchin tilapia was in the Indian River system in 1980 near Satellite Beach, Brevard County (Dial and Wainright 1983). The species is now well established in Brevard County, in the estuary, in canals near Satellite Beach, and in the Indian and Bananna rivers from Merritt Island southward to Canova Beach, a distance of 27 km (Dial and Wainright 1983). The species was abundant in shallow estuarine waters, coastal lagoons, and canal systems (Dial and Wainright 1983) where it prefers quiet backwater habitats with aquatic vegetation and mucky, organic substrate (Jennings and Williams 1992).
Whether the establishment of this species on the east coast of Florida was the result of released fishes from local fish farms, transplanted fishes by commercial fishermen from the west coast of Florida to establish a fishery, released fishes by anglers for bait, or escaped fishes from the Satellite Beach reflection pool in front of the Civic Center is not known (Jennings and Williams 1992). The distribution of the species on the east coast of Florida in August 1990 was from Cocoa Beach to just south of the Indian Harbor Beach, Brevard County. The southern edge of the range is presently near Vero Beach.
The temperature tolerance of this species depends on the ambient water temperature before the species is subject to the colder water temperature, the rate of temperature change, the length of exposure, and the salinity (Snelson and Bradley 1978; Snodgrass 1991). Stauffer et al. (1984) found the lower lethal temperature was 15 C. Shafland and Pestrak (1982) found it was 10.3 C, whereas Jennings (1991) reported that death of the blackchin tilapia occurred at 10 C. Shafland and Pestrak (1982) and later Jennings (1991) concluded that the northern expansion of the blackchin tilapia above the Indian River system is limited by cold water temperature in winter but that southern expansion of its range is probable because of the absence of physical barriers. Similar to the blackchin tilapia population on the west coast of Florida, the east coast population can be expected to expand inland as the population expands to the south. Its impact on the invaded marine, estuarine, and freshwater ecosystems is unknown but could be significant. The native habitat of the blackchin tilapia in Africa is in brackish lagoons and estuaries. The species can tolerate salinities to at least 100 ppt and produced viable offspring in salinities from 0 to at least 35 ppt. (Jennings and Williams 1992). In closed lagoons, it acclimates to hypersaline conditions (Pauley 1976).
Temperature tolerance tests at different salinities indicated that the blackchin tilapia does not survive the winter water temperature north of its present range except for short periods of time during mild winters (Jennings 1991). Populations of this species that find a source of warm water such as a warm spring or power plant effluent can overwinter every year.
Along the east coast of Florida, this species is taken by cast netting, gillnetting, and hook and line and has entered the commercial fishery (Dial and Wainright 1983). However, the value of the present fishery for this species is unknown. No studies have been conducted to determine the impact on the native marine, estuarine, or freshwater ecosystems as the species spreads southward.
Mozambique Tilapia (Tilapia mossambica; Peters). This species is established in the saline parts of the Bananna River near Cocoa Beach, Brevard County (Dial and Wainright 1983), and in brackish water areas of southeastern Florida. The populations in Brevard County probably originated from escaped or released fishes from fish farms or aquarium dumps (Courtenay et al. 1974; Dial and Wainright 1983). One population was probably the result of a developer's release to control plants (Courtenay et al. 1984). No ecological or life history studies have been conducted to determine the species' actual or potential impacts on the receiving ecosystems.
Spotted Tilapia (Tilapia mariae; Boulenger). This species is established throughout most of eastern and central Dade County northward into southern Broward County (Hogg 1974; Courtenay and Hensley 1979b, 1980; Courtenay 1984). Hogg (1974, 1976 a,b) reported that the fish was accidentally or intentionally released by fish farms. The origin of the estuarine populations was the downstream movement of fishes from freshwater into brackish water. Information about the impact of this species on native populations or about the potential range of this species is not available. Cold winter temperatures without a source of warm-water refuge stop the fishes' expansion northward, but no barriers impede its spread to the south. In freshwater, the spotted tilapia successfully competes against smaller native fishes. It has spread throughout Broward County and into the Everglades.
