In the development of individuals sex can be 

 detennined easily when they reach 6 mm. c.l., 28 

 mm. t.l. At this length females can be distinguished 

 from males by the endojjods of the first pair of 

 pleopods, which are relatively shorter and nar- 

 rower, and by the presence of two protuberances 

 on sternite XIV, which are minute but clearly dis- 

 tinct. At 18 mm. c.l., 86 mm. t.l., the median flagel- 

 lum of the male bears a few long processes, at 21 

 mm. c.l., 96 mm. t.l., it has small processes, and at 

 23 mm. c.l., 109 mm. t.l., its longer and shorter 

 processes are well developed. The sizes given above 

 are the minimum at which the antennular proc- 

 esses, in males, have attained the respective stages 

 of development. 



GROWTH 



Growth studies in Penaeus shrimps are diffi- 

 cult because of the variation in rate of increase 

 according to size and sex of individuals as well as 

 during the different seasons of the year. After 

 rearing shrimp in ponds, Johnson and Fielding 

 (1956) estimated that white shrimp attain a total 

 length of about 80 mm. 2 months after hatching. 

 Gunter (1950) had previously reported a gix)wth 

 rate of 25 to 40 mm. per month from 28 to 100 

 mm. t.l. in inshore water adjacent to the Gulf of 

 Mexico, and Viosca (1920) estimated a montlily 

 growth of about 25 mm. for shrimp with 30 to 

 150 mm. t.l. In Mobile Bay, Ala., Loesch (1965) 

 found that white shrimp increase 12 to 27 mm. 

 a month in winter, 18 to 31 mm. in summer, and 

 the "very young" may grow as much as 65 mm. 

 per month in summer. Williams (1955a) calculated 

 that inshore white shrimp in North Carolina grow 

 about 36 mm. per month during the summer, and 

 Joyce (1965) estimated that white shrimp in 

 northeast Florida grow an average of 35 mm. per 

 month. Lindner and Anderson (1956) concluded 

 that individuals 100 mm. long reached 141 mm. 

 in 2 months — an average increase of 20.5 mm. per 

 month. Lindner and Anderson (1956) also showed 

 that shrimp grow rajaidly through the sjaring to 

 early fall. Klima (1964) estimated that in Louisi- 

 ana waters during the fall wjiite shrimp grow from 

 120 mm. to 159 mm. in 2 months, an average of 

 about 19.5 mm. per month, whereas larger shrimp 

 grow very little. Growth is negligible during the 

 winter, a conclusion reached by Lindner and 

 Anderson (1956) for all populations, by Kutkuhn 

 (1962) for the Louisiana off.shore population, and 



by Joyce (1965) for the northeast Florida 

 pojDulation. 



Kutkulm (1962) estimated that the rate of 

 weight increase is relatively low in small shrimp, 

 reaches a maximum in the middle of the size range, 

 and then decreases progressively with further in- 

 crease in size. He found that gi'owth also varies 

 considerably from year to year; one age class 

 showed a 30-percent increase from November 

 through April, whereas the corresponding age 

 class in the previous year showed a 150-percent 

 increase during the same period. 



SEX DIFFERENCES IN SIZE 



The largest female examined, collected off 

 mouth of Sabine River, Tex., is 60 mm. c.l., 200 

 mm. t.l.; the largest male, collected off Bayou 

 Scolfield, La., is 41 mm. c.l., 175 mm. t.l. 



Sizes of females and males differ little inshore, 

 as shown in the length frequency distribution of 

 the shrimp in North Carolina (Williams, 1955a) 

 and in northeast Florida (Joyce, 1965). A sex- 

 size disparity occurs offshore, where females are 

 larger than males (Weymouth et al., 1933). In my 

 samples the differences in length between sexes do 

 not appear to be so pronounced as those shown by 

 the grooved shrimps. 



Ecology 

 FOOD 



Juvenile and adult white shrimp were reported 

 to be omnivorous by Viosca (1920), Weymouth 

 et al. (1933), Darnell (1958), and Broad (1965). 

 Their digestive tracts have been found to contain, 

 in addition to inorganic detritus and organic de- 

 bris, fragments of many different animals, par- 

 ticles of higher plants, and a variety of diatoms 

 and other algae. 



Studies by Flint (1956) of the stomach con- 

 tents of "shrimp" (some of which were probably 

 white shrimp) from Louisiana showed they were 

 scavengers. He found a great variety of fragments 

 of bryozoa, sponges, and corals and also sand 

 grains. He stated that filaments of blue-green 

 algae, lithophytic algae, and diatoms were present 

 in such quantities as to indicate that algae may 

 often serve as an imi:)ortant element of their diet. 

 This worker assumed that the jJresence of diatoms 

 "was incidental to the intake of other structures to 

 wliich they were adherent or attached." Flint also 

 noted that the contents of the intestinal tract of 

 small shrimp about 10 mm. t.l. "consisted almost 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEU8 



483 



