White shrimp, continued 



may influence this emigration is sharp drops in water 

 temperature occurring during the fall and winter (Pullen 

 and Trent 1 969). After leaving the estuaries, there is a 

 general westward movement of adult white shrimp in 

 offshore waters combined with movement to deeper 

 waters (Baxter and Hollaway 1981, Hollaway and 

 Sullivan 1982, Lyon and Boudreaux 1983). In April to 

 mid-May, white shrimp move back to nearshore and 

 inshore waters (Hollaway and Sullivan 1982). 



Reproduction 



Mode : Reproduction is by external fertilization be- 

 tween sexually dimorphic male and female individuals 

 (Perez-Farfante 1 969, Lindner and Cook 1 970, Muncy 

 1984). Although this species has separate male and 

 female sexes (gonochoristic), hermaphroditism has 

 been reported in white shrimp parasitized by Thelohania 

 sp. (Rigdonet al. 1975). 



Mating/Spawning : The external genital organ (thelycum) 

 in female white shrimp is open, unlike those in brown 

 shrimp, making copulation possible between two hard- 

 shelled individuals (Overstreet 1978, Muncy 1984). 

 The male places a spermatophore on the female's 

 abdomen, and when eggs are released the spermato- 

 phore releases sperm fertilizing the eggs externally 

 (Perez-Farfante 1969). Spawning along the Atlantic 

 coast probably begins in May and extends through 

 September (Lindner and Anderson 1956, Williams 

 1984); in the Gulf, the season probably extends from 

 March to September or October (spring to late fall) 

 (Franks et al. 1972). Spawning occurs offshore at 

 depths of 9 to 34 m deep and peaks in the summer 

 (June-July). There is also some suggestion of limited 

 spawning within estuaries and bays (Lindner and Cook 

 1970, Whitaker pers. comm.). Females that spawn 

 early may spawn a second time in late summer or fall, 

 and possibly up to 4 times in a season (Lindner and 

 Anderson 1956, Lindner and Cook 1970, Whitaker 

 pers. comm.). The ability of shrimp over one year old 

 to spawn is unknown, but considered possible (Lindner 

 and Cook 1 970, Zein-Eldin pers. comm.). Othershrimp 

 species with similar methods of reproduction have 

 been found to spawn again in their second year. Rapid 

 temperature changes, such as the sudden increases 

 and decreases that occur in the summer and fall, seem 

 to trigger spawning (Henley and Rauschuber 198.1). 



Fecundity : A large female is estimated to produce 0.5 

 to 1.0 million eggs at a single spawning (Anderson et 

 al. 1949, Lindner and Cook 1970, Williams 1984). 



Growth and Development 



Egg Size and Embryonic Development : Egg develop- 

 ment is oviparous. Fertilized eggs are demersal, 

 nonadhesive, spherical, and are approximately 0.28 

 mm in diameter (Lindner and Cook 1970). Ripe eggs 



are 0.2 to 0.3 mm in diameter and hatch in 10 to 12 

 hours after fertilization (Klima et al. 1982). 



Age and Size of Larvae : Eggs hatch into planktonic 

 nauplii approximately 0.3 mm TL (Klima et al. 1982). 

 Larvae transform through 5 naupliar stages, 3 

 protozoeal stages and 3 mysis stages (Perez-Farfante 

 1969). The length of larval life is from 10 to 12 days, 

 depending on local food, habitat, and environmental 

 conditions. They enter the estuaries as postlarvae at 

 total lengths (TL) of approximately 7 mm. Rapid growth 

 rates of 20-40 mm/month occur in nursery areas (Wil- 

 liams 1955a, Lindner and Anderson 1956, Perez- 

 Farfante 1 969, Lindner and Cook 1 970). Growth is far 

 more strongly affected by changes in temperature than 

 salinity (Zein-Eldin and Griffith 1969), with little or no 

 growth occuring below 18°C (Zein-Eldin and Renaud 

 1986). Postlarvae develop into juveniles at about 25 

 mm TL (Christmas et al. 1976). 



Juvenile Size Range : Juveniles can attain lengths of 98 

 to 146 mm TL in 4 to 6 weeks after entering estuarine 

 areas (Zein-Eldin and Renaud 1986). Emigration of 

 subadults occurs through the summer and fall at a size 

 of 100 to 120 mm TL. Sexual maturity is generally 

 reached at 140 mm TL in the northern Gulf of Mexico 

 (Perez-Farfante 1969, Lindner and Cook 1970). 



Age and Size of Adults : The white shrimp has a life 

 expectancy of 18 months, although some have been 

 maintained in the laboratory for 3 to 4 years (Klima et 

 al. 1982). Females become sexually mature at about 

 165 mm TL and ripe sperm first appears in males at 

 about 119 mm TL (Burkenroad 1939, Lindner and 

 Cook 1970). 



Food and Feeding 



Trophic Mode : White shrimp are omnivorous at all life 

 stages, but may depend more heavily on plant matter 

 than animal matter (McTigue and Zimmerman 1991). 

 Larval white shrimp are planktivorous, while adults and 

 juveniles are scavengers. 



Food Items : Penaeid larvae subsist on egg yolk until 

 the Protozoea I stage when active feeding begins 

 (Lindner and Cook 1 970). Larvae are reported to feed 

 on plankton and suspended detrital material, and in the 

 laboratory, they have been successfully fed micro- 

 scopic green algae and brine shrimp nauplii. Both 

 juveniles and adults are omnivorous. Juveniles com- 

 bine detrital feeding with scavenging on the bottom 

 sediment. As they mature, they combine predation 

 with detrital feeding. Foods consist of detritus, insects, 

 annelids, gastropods, and fish, and copepods, bryozo- 

 ans, sponges, corals, filamentous algae, and vascular 

 plant stems and roots (Darnell 1958, Perez-Farfante 

 1969, Christmas and Etzold 1977). 



76 



