Weight-Length Relation 



The shrimp were separated into two cate- 

 gories — (1) ovigerous females and (2) males 

 and nonovigerous females combined. I had 

 insufficient time to determine the sex of the 

 nonegg bearing shrimp. Live shrimp (major 

 chelae removed) were measured and weighed. 

 I made no attempt to find the effect of the 

 holding period on weight — any effect probably 

 was insignificant, since the shrimp were fed 

 by their keepers, and holding did not diminish 

 the shrimps' voracious cannibalistic appetite. 



If fewer than 100 shrimp were weighed and 

 measured in any monthly sample, I used the 

 entire sample in my calculations; if more than 

 100 were weighed and measured, only 100 were 

 used. The weight-length relation of 100 shrimp 

 was derived from the 15 shortest, the 15 long- 

 est, and 70 shrimp taken at random from the 

 sample. The weight-length relation is de- 

 scribed by the equation Log W = Log a + b 

 Log L, which is the logarithmic transformation 

 of W = aLb, where W = weight in grams and 

 L = body length in millimeters. 



The weight-length relations by month (table 

 5) were plotted on logarithmic paper, but dif- 

 ferences were small. Samples were then 

 grouped to derive the relation between weights 



Table 5. — Weight-length relation of M. vollenhovenii 

 caught in Liberia, 1952-53 



Date 



Shrimp 

 examined 



b 



Log a ( — ) 





No. 







Males and 









nonovigerous 









females : 









December 1952 



100 



3.233760 



5.104878 



January 1953 



69 



3.103854 



4.900119 



February, Marc 



M 







and April 19c 



35 







May 1953 .... 



100 



2.888036 



4.430167 



June 1953 



100 



2.942819 



4.528751 



July 1953 



100 



2.923373 



4.488341 



August 1953 . . 



80 



3.009451 



4.668415 



September 1953 



100 



3.204240 



5.059211 



October 1953 . 



100 



3.077283 



4.791176 



November 1953 



100 



3.069324 



4.750091 



December 1953 



62 



3.229206 



5.099838 



Total . 



911 



3.093213 



4.829690 



Ovigerous female: 









1952-53 



181 



3.011392 



4.656069 



o 



<2 40 



5 



. 





- x--x Ovigerous Females, N=181 



• 



' •— • Males & Nonovigerous 





Females. N = 911 , 





*/ 





// 





V 





1 





II 





1/ 





II 





1/ 





1/ 





1/ 





// 





// 





'/ 





// 





// 





// 





// 





sS 





^v / ^ 













. •> — -T i 1 1 1 1 1 1 1 L 



1— — 1 



TOTAL LENGTH (MM.) 

 Figure 6. — Weight-length relation of commercial 

 shrimp, M. vollenhovenii, for ovigerous females 

 (range 47-131 mm., Log W = -4.656603 + 3.011392 

 Log L) and males and nonovigerous females (range 

 39-150 mm., Log W = -4.829560 + 3.092213 Log L) . 

 Shrimp were captured in the lower St. Paul River, 

 Liberia, 1952-53. 



and lengths for the ovigerous females and for 

 the combined males and nonovigerous females. 

 Ovigerous females were slightly heavier than 

 males and nonovigerous females (fig. 6). 



Only a slight difference was seen between 

 the weight-length relation of M. vollenhovenii 

 and the weight-length data of pond-cultured 

 M. rosenbergii given by Ling (1967a). The 

 growth differential between the two species is 

 exceedingly different — M. rosenbergii reached 

 155 m. in 7 months. 



Fecundity and Spawning 



I estimated the fecundity by counting the 

 number of eggs that displaced a known vol- 

 ume of water. Because the fecundity of crus- 

 taceans differs with size, the sample was se- 

 lective in that small shrimp (76-82 mm.) and 

 large shrimp (101-113 mm.) were used to es- 

 timate numbers of eggs per female. In small 

 shrimp 1,555 to 1,785 eggs displaced 0.1 ml. 

 of water; in large shrimp 850 eggs displaced 

 0.1 ml. of water. Estimates of the numbers of 

 eggs carried externally by the small shrimp 



