Gunter (1950) and Kutkuhn (1962) in the same 

 region and Joyce (1965) in northeast Florida 

 found two main broods amiually. 



Temperature is a major factor controlling 

 spawning. Lindner and Anderson (1956) stated 

 that spawning seems to be started more by rapid 

 changes in temperature than by attainment of an 

 optimum temperature; sudden warming in the 

 spring apparently triggers spawning, which ap- 

 pears to end when the temperature declines ab- 

 iiiptly in the fall, even though the water is warmer 

 at this time than at the begimiing of the spawning 

 season. 



Evidence is considerable that P. sefiferu.s may 

 spawn more than once during its life span. King 

 (1948) found that immediately after the first 

 spawning the spent ovaries grow considerably. He 

 suggested that females which spawn early in the 

 season may develop a second crop of eggs and 

 si>awn again tlie same season. Studies of ovaiy 

 development in the northwestern Gulf by William 

 C. Eenfro and Kobert F. Temple (personal com- 

 munication) indicate that recovery and redevel- 

 opment are fairly raj^id, at least dui'ing the 

 summer; recently spent ovaries contained large 

 numbers of rapidly developing ova together with 

 ripe ova in the process of teing absorbed. Accord- 

 ing to Lindner and Anderson (1956), the percent- 

 age of females with spent ovaries is very Ioav in 

 Louisiana waters from June through August. They 

 suggested shrimp could spawn four times in a 

 season. 



SEX RATIO 



The general male-female ratio appeai-s to be 

 about 1:1; considerable variation has been ob- 

 served, however. I have examined many offshore 

 samples that contained but one sex, so some segre- 

 gation by sexes may occur. 



Postembryonic Development 

 LARVAE, POSTLARVAE, AND JUVENILES 



Eggs hatch within a few hours after spawning, 

 and the young emerge as nauplii, the first of 11 

 lai-val stages. Peai-son ( 1939) was the firet to study 

 the larval development of white shrimp through 

 material found in plankton samples and by rear- 

 ing experiments. So accurate were his observations 

 that subsequent studies by Heegaard (1953) and 

 Johnson and Fielding (1956) have proved his 

 series of stages almost faultless, except that one 



mysis stage was not recognized. Harry L. Cook 

 (pei-sonal communication) observed in the labora- 

 tory that P. sctifcnis has five nauplial, three pro- 

 tozoeal, and three mysis stages. After the last mysis 

 comes the first mastigopus or first postlarv^a. 



Some investigators doubt the existence of diag- 

 nostic characters that distinguish the larvae of 

 western Atlantic Pe7ia£u.i, whereas others main- 

 tain that they can be sepai-ated. Pear-son (1939) 

 and Heegaard (1953) described the main charac- 

 teristics of various larvae of P. setifents. 



Tlie wliole larval cycle of the white shrimp was 

 found by Jolmson and Fielding (1956) to extend 

 10 to 12 days, but these authors stated that "the 

 duration of the metamorphic i^eriod is not fixed, 

 but depends to some extent on local conditions of 

 food and habitat." At the end of this period the 

 planktonic lar\ae have reached the postlarval 

 stage. Early ].x)stlarvae are planktonic and live off- 

 shore. As they grow they move toward and finally 

 enter inshore waters. 



Williams (1959) distinguished postlarvae imder 

 12 mm. t.l. of P. setifents, P. a. aztecus, and P. d. 

 duorarum on the basis of two characters recognized 

 by Pearson (1939) — the relative lengths of the 

 rostiiun and tliird pereopod — as well as by body 

 size and shape of the distal end of the antennal 

 scale. These characters have proved to be helpful, 

 although it seems that sometimes their range of 

 variation in the various species overlaps. Accord- 

 ing to Baxter and Renfro (1967), those features 

 allow tlie identification of wliite shrimp postlarvae 

 up to 10 mm. t.l. in the Galveston area. 



Recently, Zamora and Trent (1968) reported 

 that in postlarv^il white shrimp the keel of the 

 sixth abdominal somite is smooth, lacking setae, 

 whereas that of postlarval brown and pink shrimps 

 bears setae. The presence or absence of setae on the 

 keel considerably facilitates the separation of the 

 postlarvae of white shrimp from those of the pink 

 and brown shrimps. 



Small Penaeus are considered juveniles when 

 they have attained the ultimate rostral tooth for- 

 mula. Freshly caught juveniles of the white shrimp 

 often have widely spaced body chromatojjhores 

 and, thus, have a lighter color than those of sym- 

 patric pink and brown shrimps; this character, 

 however, has only limited diagnostic value since 

 shrimp collected from dark substrates tend to be 

 dark. Juveniles 18 mm. t.l. have no long adrostral 

 sulci and so are easily separated from the grooved 

 Penaews. 



482 



U.S. FISH AND WILDLIFE SERVICE 



