LENGTH-WEIGHT RELATION IN THE COMMON OR WHITE 

 SHRIMP , PENAEUS SETIFERUS 



In order to determine the size at 

 which a species can be most profitably 

 taken, the relation between increase in 

 mass weight of a shrimp population through 

 growth and recruitment and decrease through 

 mortality must be known. Sxformation about 

 length and weight as attributes of growth 

 are essential in understanding this rela- 

 tion. The length-weight relations for 

 common or white shrimp, Penaeus setif erus 

 (Linnaeus), were determined from measure- 

 ments of lengths and weights of 14,284 

 specimens secured over a 1-year period in 

 Texas. Material was obtained during each 

 month of the year. Measurements of total 

 length (from tip of rostrum to tip of tel- 

 son) were taken to the nearest millimeter 

 and weights to the nearest tenth of a 

 grajn. Table 1 presents the monthly length- 

 weight distributions showing separately 

 for males and females the number of speci- 

 mens exEunined in each 5- mm. length interval 

 and the average weight in grams. 



Some differences in the length-weight 

 relation occur seasonally owing primarily 

 to chcinges in the body proportions of the 

 shrimp. The bodies of the older shrimp 

 tend to thicken, ajid their weights are 

 greater in proportion to length than are 

 those of younger shrimp. This change 

 appears to be associated with maturity and 

 was most noticeable during July and August 

 when both mature shrimp, about 1 year old, 

 and immature young-of-the-year were present 

 in the catches in appreciable numbers. The 

 differences in weight for mature and imma- 

 ture shrimp of the same length are shown 

 in table 2 and figure 1. Where the two 

 length rcinges overlap (148 to 163 mm.) it 

 is readily apparent that the mature shrimp 



average considerably heavier (about 3 

 grams) than immature shrimp of the same 

 length. 



In figure 1 we have also plotted the 

 length-weight relation of all shrimp over 

 100 mm. total length taken during the 

 period of September through March (table 3). 

 These shrimp were largely immature. The 

 length-weight relation for these shrimp 

 from September to March was identical with 

 that of the immature for July-August over 

 the overlapping size ranges (103 to 163 mm.). 

 In shrimp over 170 mm. total length the 

 difference between the upper and lower 

 curves decreases, and it disappears entirely 

 between about 180 and 190 mm. We interpret 

 this to mean that all shrimp over 190 mm. 

 total length were mature and that between 

 170 and 190 mm. there were increasing pro- 

 portions of mature or maturing shrimp. 



The general practice in the shrimp 

 industry is to refer to the size of shrimp 

 in terms of the number required to make 1 

 pound. Two systems are in use — the number 

 of whole shrimp per pound and the number 

 of shrimp tails per pound. The latter is 

 more generally used. Since the original 

 mesisurements were made for whole shrimp, 

 the factor 1.68 has been applied to the 

 number of vrtiole shrimp per pound to obtain 

 the approximate number of tails per pound. 

 These data are presented in table 4 and in 

 figure 2 and 3. Most of the commercial 

 catch of white shrimp is composed of shrimp 

 between 3 and 8 inches in total length. 



Kenneth H. Mosher contributed much 

 in the collection of data which made this 

 study possible. 



