Common snook, continued 



Salinity - Eggs and Larvae: Eggs and larvae have been 

 raised in the laboratory in salinities from 30 to 38%o 

 (Shafland and Koehl 1979, Lau and Shafland 1982, 

 Tucker 1986). Both appear to prefer polyhaline to 

 euhaline salinity ranges and are unable to develop in 

 fresh water. Larvae at 1 4 days of development can be 

 successfully transferred to fresh water and are consid- 

 ered euryhalineatthis point (Ageretal. 1976, Shafland 

 and Koehl 1979). Field studies show a significant 

 relationship between larval size and salinity, with larger 

 larvae occurring in lower salinities (Tolley et al. 1 987). 

 Snook larvae have been collected from Naples Bay, 

 Florida, in salinities ranging from 1 4.8 to 33.5%o (Tolley 

 etal. 1987). 



Salinity - Juveniles and Adults: Both juveniles and 

 adults are euryhaline, and have been reported from a 

 salinity range of 0.0 to 36%o (Hildebrand 1 958, Marshall 

 1958, Springer and Woodburn 1960, Tabb and Man- 

 ning 1961, Tabb et al. 1962, Gunter and Hall 1963, 

 Gunterand Hall 1965, Bryan 1971, Martin and Shipp 

 1 971 , Dahlberg 1 972, Fore and Schmidt 1 973, Cooley 

 1974, Kushlan and Lodge 1974, Gilmore et al. 1983, 

 McMichael et al. 1989). Adult snook are more often 

 associated with moderate to higher salinities within this 

 range (Marshall 1958, Fore and Schmidt 1973, Sea- 

 man and Collins 1983, Palik and Kunneke 1984). On 

 the east coast of Florida, juvenile snook <50mm con- 

 sistently occur at lower salinities, whereas those 

 >150mm are generally found in higher salinity waters 

 (Gilmore etal. 1983). Snook are relatively widespread 

 in freshwater areas in Florida, and have been collected 

 in Lake Okeechobee, coastal rivers, the Big Cypress 

 Swamp, and at several locations in the Everglades 

 (Loftus and Kushlan 1987). Physiological studies of 

 juveniles indicate they can osmoregulate at salinities 

 between and 45%o in a manner similar to other 

 brackish water fishes (Quintero and Grier 1 985). More 

 than 70% of seing-caught and 90% of trawl-caught 

 specimens taken in the Little Manatee River from 1 988 

 to 1991 were taken at salinities less than 5% . Maxi- 

 mum numbers were taken during October and Novem- 

 ber. Changes in blood osmolality and gill morphology 

 of juvenile snook after acclimation at various salinities 

 (0, 15, 30, and 40%>) has been studied (Quinterro and 

 Torres 1993). The chloride cells within the gills ap- 

 peared to be metabolically active regardless of the 

 acclimation salinity. 



Dissolved Oxygen: Dissolved oxygen (DO) level may 

 limit the distribution of this fish in confined or isolated 

 marsh habitats (Gilmore et al. 1983). Juvenile snook 

 have been collected in impounded wetland habitats 

 associated with the Indian River Lagoon with DO levels 

 of less than 1.0 ppm (no ref). Peterson and Gilmore 

 (1991) found an ontogenetic change in a juvenile 

 snook's ability to survive reduced oxygen levels which 



correlated well with the habitat shift noted by Gilmore 

 et al. (1983). Small juveniles may also use aquatic 

 surface respiration to utilize the well-oxygenated sur- 

 face film during hypoxic events (Peterson et al. 1 991 ). 



Movements and Migrations : Snook is a relatively non- 

 migratory, inshore species (Volpe 1959, Moe 1972). 

 Apparently this fish has a broad inshore range and 

 moves freely in this area, as conditions permit, in short 

 coastwise movements (Moe 1 972, Tucker 1 986). Eggs 

 and larvae are carried by currents or swim to nursery 

 areas where they remain until maturity. It has been 

 suggested that the optimal salinity for activity changes 

 with development in juveniles from freshwater to isos- 

 motic levels to match, or even determine, their gradual 

 migration to higher salinities (Perez-Pinzon and Lutz 

 1991). Movements from estuaries and fresh water 

 tributaries to spawning areas just offshore can be 

 considered a limited spawning migration (Moe 1972, 

 Tucker 1986). Some southerly movements in re- 

 sponse to falling water temperature have been noted 

 (NOAA 1 985). Juvenile snook exhibit a habitat speci- 

 ficity which changes as the fish grow older, resulting in 

 localized movements. Adult habitat requirements are 

 not as narrow as those of juveniles, although limited 

 movement occurs throughout the life cycle (Gilmore et 

 al. 1983). In a study of Tampa Bay, Florida, most 

 juvenile snook were concentrated in two tributaries, the 

 Alafia and Little Manatee Rivers (CES 1992). Adult 

 snook were also concentrated in tributaries, except in 

 the spring when they were scattered throughout 

 nearshore areas of Tampa Bay. In another study of 

 Little Manatee River, Florida, most juveniles were 

 found along the shoreline at two marginal creek/cove 

 sites (Matheson and Rydene 1993). 



Reproduction 



Mode : This species can be considered a protandric 

 hermaphrodite, suggested by skewed sex ratios that 

 significantly favor small males, and the absence of age 

 and 1 females (Taylor and Grier 1993, Taylor pers. 

 comm.). Comparisons of the chromosomes of males 

 and females do not show differences in chromosomatic 

 size or number (Ruiz-Carus 1993). The banding 

 patterns on the chromosomes supported the hypoth- 

 esis of protandric hermaphroditism. Examination of 

 more than 4,100 snook gonads confirmed that snook 

 undergo sex reversal (Taylor and Grier 1 993). For all 

 snook <500mm and under age 4 the sex ratio was 

 skewed in favor of males (6.1 M:1 .OF), whereas for fish 

 >800mm and over age 7 the sex ratio favors females 

 (1 .0M:3.2F). Direct evidence from pond-held juvenile 

 males demonstrates that female common snook are 

 derived from post-mature males (Taylor pers. comm.). 

 Fertilization is external, by broadcast of milt and roe. 



196 



