deep from March to July, but were absent in Au- 

 gust, scarce in September, and absent again in 

 October and December. According to de Oliveira 

 (1950), juveniles are abundant in Baia de Guana- 

 bara, Brazil, in January and February (during 

 the summer) and da Silva (1965) collected larvae 

 and juveniles in Baia de Sepetiba, Brazil, in 

 March and April, or in late summer and early fall. 



GROWTH 



Little information is available on growth of this 

 species. It has been stated (Anonymous, 1962) 

 that in Guyana individuals kept in ponds grew 

 from 25 nnn, t.l. to 200 to 225 mm. t.l. through 

 a period of 7 to 8 months. Ewald (1965c) estimated 

 that in Lake Maracaibo — where juveniles and sub- 

 adults live — shrimp increase up to 50 mm. monthly. 

 Finally, Khandker (in press) found that in La- 

 giuia de LTnare, Venezuela, P. schmittl grew an 

 average of 1 mm. per day from July through 

 October. 



SEX DIFFERENCES IN SIZE 



Females attain a greater length than males. The 

 maximum reported female length is 235 mm. t.l. 

 (Davant, 1963). The largest male measured was 

 43 mm. c.l. (about 175 nun. t.l.) ; it was taken in the 

 Gulf of Venezuela by Ewald (1965c). 



In inshore samples males and females are about 

 the same size, whereas in the offshore material 

 some of the females are larger than the largest 

 males. This sex-size disparity in the white shrimp 

 was noticed in material obtained by Loesch (1962) 

 and in the material I examined. 



Ecology 



FOOD 



White shrimp are omnivorous. They ingest algae, 

 organic debris and sand, as well as a variety of 

 animals. Among the animal remains found in their 

 digestive tract are those of nematodes, annelids, 

 mollusks, and crustaceans. 



SUBSTRATE 



P. schmitti offshore lives on soft bottoms of mud 

 and silt, often mixed with coral sand and small 

 fragments of mollusk shells. Although not numer- 

 ous, these shrimp also occur in patches pre- 

 dominantly of sand on rock bottoms. In estuarine 

 water, late postlarvae and juveniles live on muddy 

 bottoms where there is abundant vegetation or 

 organic debris. 



DIEL CYCLE 



In some areas — Gulf of Venezuela (Ewald, 

 1965c) and southern Cuba (Perez Farfante, 

 1954b; Perez Farfante et al., 1961)— the capture 

 of adidts day and night indicates that they are 

 active at all hours, but in Honduras and Nicaragua 

 they are caught almost exclusively during the day. 

 In Cuba, juveniles and subadults of P. schmitti are 

 fished m estuarme waters mostly at dawn or dur- 

 ing the morning. According to Ewald (1964), 

 white shrimp are fished commercially in Lake 

 Maracaibo during the last hours of the night, and 

 Boschi (1963) stated that they are taken in the 

 lagoons of Cananeia, Brazil, in the first hours of 

 the morning. It, thus, seems as if the young shrimjD 

 are more active at dawn and the hours immediately 

 after. 



MOVEMENTS 



The larvae of P. schmitti move from the sea, 

 where hatching occurs, to brackish waters where 

 they arrive as postlarvae. Khandker (in press) re- 

 ported that postlarvae appear at the seashore near 

 Laguna de LTnare, Venezuela, in June and July 

 and begin to enter the Laguna in July at an aver- 

 age length of 8.5 mm. t.l. Ewald (1965c) collected 

 thousands of postlarvae up to 10 mm. t.l. in the 

 Estrecho de Maracaibo, and the occurrence of these 

 postlarvae indicates a movement from the En- 

 senada de Calabozo, where mature females are 

 found, toward Lake Maracaibo, one of the most 

 important nursery grounds of the white shrimp. 



The juveniles grow rapidly in the rich estuarine 

 waters, reaching a size and abundance that makes 

 commercial fishmg highly profitable. At the end 

 of a few months — 6 to 9 in Lake Maracaibo 

 (Ewald, 1965c) — they move back to sea where the 

 life cycle is completed. An indication of the sea- 

 ward migration of P. schmitti was given by Ewald 

 (1965c), who found that the largest as well as the 

 average sizes of both males and females in Lake 

 Maracaibo were smaller than those in the Gulf of 

 Venezuela. This observation suggests that as the 

 shrimp grow they move from the almost fresh wa- 

 ters of the lake to waters of higher salinity in the 

 Gulf. With regard to size distribution in sea wa- 

 tei-s, Perez Farfante (in press) in Cuba fomid a 

 gradient fi'om shallow to deep water; the largest 

 specimens were farthest from shore and in the 

 deepest water. 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



497 



