Spot, continued 



Temperature - Juveniles 



and Adults: Spot tolerate temperatures from 1 .2° to 

 36.7°C; however, extended periods of low tempera- 

 tures have resulted in dead or stunned fish. Death due 

 to temperature is a function of size, acclimation and 

 rate of temperature drop (Benson 1 982). Juvenile spot 

 are reportedly more tolerant of cold than adults. Large 

 numbers of adults are found between 25° to 30°C 

 (Warren and Sutter 1982). 



Salinity - Eggs and Larvae: Laboratory spawned eggs 

 have developed at 30 to 35%o (Powell and Gordy 

 1980). Larvae have been collected in the field from 6 

 to 36%o, and appear capable of tolerating a wide range 

 of estuarine salinities (Warlen and Chester 1 985, Cowan 

 and Shaw 1988, Killam et al. 1992). They have been 

 reared successfully in the laboratory at 30 to 35%o. 



Salinity - Juveniles and Adults: Spot is a euryhaline 

 species. Juveniles have been found from to 36.2%o 

 (Kelley 1965, Wang and Raney 1971, Wagner 1973, 

 Pineda 1975, Lee et al. 1980, Benson 1982). They 

 occur in greater numbers at salinities above 1 0% o , and 

 are less abundant in freshwater areas (Killam et al. 

 1992). Adults seem to prefer a more polyhaline envi- 

 ronment than juveniles. Although they have been 

 found from to 60% o (Hildebrand and Cable 1930, 

 Thomas 1 971 , Powell and Gordy 1 980), large numbers 

 occur most often from 1 5%oto 30%<= (Warren and Sutter 

 1982). 



Dissolved Oxygen: This species is very tolerant of low 

 dissolved oxygen (DO) conditions and has been found 

 in waters with DO less than 2 parts per million (ppm) 

 (Killam etal. 1992). It is most common in waters where 

 the DO exceeds 4 ppm. For juvenile spot acclimated 

 to 28° C, 1 and 96 hour LC50s were determined to be 

 0.43 and 0.60 ppm respectively. 



Migrations and Movements : Adults migrate seasonally 

 between estuarine and coastal waters. They enter 

 bays and sounds in spring and move offshore in fall and 

 winter to spawn (Hildebrand and Schroeder 1928, 

 Pearson 1929, Hildebrand and Cable 1930, Gunter 

 1945, Dawson 1958, Kelley 1965, Perry 1970, Franks 

 et al. 1972, LeBlanc et al. 1991) and avoid cold tem- 

 peratures (Christmas and Waller 1973, Huish and 

 Geaghan 1987). Post-spawning fish have been col- 

 lected in nearshore waters, and it is possible that adults 

 remain offshore after spawning although few are taken 

 in these areas by bottom trawling (Gunter 1 945, Dawson 

 1958, Hales and Van Den Avyle 1989). Larvae are 

 probably carried by longshore currents or by direct 

 across-shelf transport into nearshore waters, and into 

 estuarine areas by tidal flow (Cowan and Shaw 1988, 

 Mercer 1989). Immigration into estuaries of post- 

 larvae begins in December and continues through May 



(Joseph 1972, Warren and Sutter 1982, Cowan and 

 Shaw 1988, Mercer 1989). A pattern of recruitment 

 along the sandy shorelines and seagrass beds of 

 Tampa Bay have been observed for postlarvae less 

 than 20 mm SL (Killam et al. 1992). These protected 

 regions appear extremely beneficial in promoting the 

 rapid growth of postlarvae. Juveniles move up into low 

 salinity headwater areas and may ascend brackish 

 water to fresh water during the spring and summer 

 (Hildebrand and Cable 1930). Older fish tend to seek 

 out deep, higher salinity waters in bays, and begin to 

 emigrate from estuaries in May or June, becoming 

 absent by late fall (Nelson 1 967, Parker 1 971 , Warren 

 and Sutter 1 982). Emigration occurs when they reach 

 total lengths (TL) of about 60 (Townsend 1956) to 88 

 mm, or after about 8-9 months (Kilby 1955, Wagner 

 1973, Killam et al. 1992), and may be a response to 

 seasonal temperature declines (Sheridan 1 979). Some 

 adults may not migrate back to inshore waters, but 

 remain in deep waters (50-91 m) in the Gulf (Perry 

 1970). 



Reproduction 



Mode : This species has separate male and female 

 sexes (gonochoristic). Fertilization is external, by 

 broadcast of milt and roe into the water column, and the 

 degree of fertilization is determined by the density of 

 spawning individuals (Killam et al. 1992). Egg devel- 

 opment is oviparous. 



Spawning : Spawning occurs from late fall to early 

 spring offshore in moderately deep water over the 

 continental shelf (Townsend 1956, Dawson 1958, 

 Nelson 1967, Wang and Raney 1971, Sabins and 

 Truesdale 1 974, Allshouse 1 983, Mercer 1 989, Killam 

 et al. 1992) with possibly some activity near beaches 

 and passes (Pearson 1 929, Music 1 974). Spawning in 

 the Gulf waters off Louisiana occurs from near midshelf 

 (about 65 km) out to 1 75 km from the coast (Cowan and 

 Shaw 1988), although spawning activity appears to 

 decrease in the offshore direction (Sogard et al. 1 987). 

 Spawning seasons in the Gulf of Mexico are: from 

 October through March or April in the Tampa Bay 

 region of Florida (Killam et al. 1992); in the northern 

 Gulf off Alabama, probably from December to at least 

 late February (Nelson 1 967); in Louisiana waters from 

 Novemberthrough March (Cowan and Shaw 1 988); off 

 Texas late November to April, with peaks from Decem- 

 berto February (Pearson 1 929, Allshouse 1 983). Based 

 on the presence of larval spot in the northern Gulf of 

 Mexico, it can be inferred that spawning occurs Octo- 

 ber through April, with a peak from December through 

 January (Ditty 1 986, Ditty et al. 1 988). Sheridan et al. 

 (1 984) suggested a late fall peak for fish in the northern 

 Gulf, but no winter samples were taken. Spot held in a 

 laboratory only spawned at temperatures between 

 17.5 to 25.0° C. 



271 



