30 L. Stanton Hales, Jr. 



Marks resembling annuli were not visible on the otoliths or scales of 

 any specimens. The coloration, lack of gonadal development, and 

 absence of annuli on any scales or otoliths suggest that all blue tilapia 

 collected in the tidal creek were young of the year. 



Temperature and salinity at this site were 20-29° C and 2-20 ppt, 

 respectively. During at least two rainstorms (22-23 July and 9 August), 

 salinity dropped below 1 ppt. Other species collected in this creek were 

 American eel, Anguilla rostrata Lesueur; sheepshead killifish, Cyprino- 

 don variegatus Lacepede; mummichog, Fundulus heteroclitus (L.); 

 mosquitofish, Gambusia affinis (Baird and Girard); sailfin molly, 

 Poecilia latipinna (Lesueur); striped mullet, Mugil cephalus L.; and 

 freshwater goby, Gobionellus shufeldti (Jordan and Eigenmann). 



DISCUSSION 



A self-sustaining population of blue tilapia does not appear to be 

 established at the present time; however, physiological characteristics of 

 this species may facilitate its establishment in the Skidaway River. 

 Although different measures of lethal temperature range from 6 to 12°C 

 (Shaflund and Pestrak 1982, Zale 1984), the blue tilapia tolerates 

 temperatures as low as 5°C in fresh water for brief periods (McBay 

 1961) and requires only 20°C for spawning (McBay 1961). Temperatures 

 lower than 5°C seldom occur in the Skidaway River, and temperatures 

 above the minimum for spawning occur from April through October in 

 most years (D. Miller, University of Georgia Marine Extension 

 Aquarium, personal communication). Blue tilapia are not only tolerant 

 of high salinity, but also grow well and reproduce in brackish waters 

 (Loya and Fishelson 1969, Trewavas 1983). In addition, blue tilapia are 

 tolerant of poor water quality, including high ammonia (Redner and 

 Stickney 1979). Conditions suitable for the growth and reproduction of 

 blue tilapia are present throughout coastal waters of Georgia, including 

 estuaries. 



Although blue tilapia are not well studied in estuarine environments, 

 other aspects of the ecology of the species appear conducive to its 

 establishment in the Skidaway River. Mature individuals were not 

 collected during this study, but ripe gonads have been observed in 

 specimens as small as 58 mm standard length (Chervinski 1968). In 

 Alabama ponds, females began to mature at 50 days and 10 cm TL 

 (McBay 1961). Those conditions of maturity, the presence of potentially 

 mature (> 58 mm SL) individuals in the Skidaway creek, and the 

 favorable growing season in coastal Georgia indicate that establishment 

 of a reproducing population in the Skidaway River estuary is a reason- 

 able possibility. The blue tilapia is established in at least one Florida 

 estuary, Tampa Bay (Courtenay et al. 1984). 



