Commercial Fishery and Biology of the Fresh-Water Shrimp, 

 Macrobrachium, in the Lower St. Paul River, Liberia, 1952-53 



By 



GEORGE C. MILLER, Zoologist 1 



National Marine Fisheries Service 



Tropical Atlantic Biological Laboratory 



Miami, Florida 33149 



ABSTRACT 



A small fishery was conducted for the large commercial fresh-water shrimp, Macrobrach- 

 ium vollenhovenii, using traps. A second smaller species, M. macrobrachion, was culled from 

 the trap catch for the fishermen's use. The estuarine fishery was seasonal (May to Janu- 

 ary) , during the period of low salinity. Cost of raw tail meats to the consumer was over 

 $1.00 (U.S.) per pound. The fishermen derived more than $7,500 from the fishery. 



Commercial shrimp, M. vollenhovenii, spawned in the estuary from May to January. 

 Fecundity was estimated at 12,000 to 45,000 eggs per female. As the embryo developed 

 the color of the egg changed from red to brown. Embryonic and larval development to 

 time of setting of M. vollenhovenii was believed similar to that of M. rosenbergii, 50 to 

 65 days. An intensive push-net fishery was conducted by women on the zero age group soon 

 after the juveniles had set. Juvenile shrimp were not caught by traps. Monthly length dis- 

 tributions indicated that the fishery was supported by age group one, which was replaced 

 at the end of the season by age group zero. Age group zero grew rapidly and reached a 

 modal length of 75 to 80 mm. in 9 months in January; and adults grew slowly and increased 

 in length to 85 to 90 mm. in May, and 100 to 105 mm. in November. The weight-length re- 

 lation of M . vollenhovenii ovigerous females was expressed by the equation Log W = — 4.656603 

 + 3.011392 Log L, and males and nonovigerous females by Log W = — 4.829560 + 

 3.092213 Log L. 



The characters used to distinguish M. macrobrachion from the commercial shrimp are 

 given. The smaller species (modal length 50 to 54 mm.), constituted 88 percent of the 

 shrimp discarded from the commercial catch. The trap fishery harvested the adults of the 

 two species, which differed considerably in length, without harm to either species. 



INTRODUCTION 



Fresh-water shrimp, Macrobrachium (fam- 

 ily Palaemonidae) , are found worldwide in 

 tropical fresh and brackish waters. Commer- 

 cial fisheries exist for many of the species 

 (Holthuis and Rosa, 1965). Interest has been 

 shown in the possibility of using fresh-water 



1 The author made this study while on loan from the 

 U.S. Fish and Wildlife Service to the U.S. Foreign 

 Operations Administration, as Technical Advisor in 

 Marine Fisheries to the Liberian Government. 



shrimp for aquaculture because of their fast 

 growth rate (Dobkin, 1967; Ling, 1967a, 

 1967b; Ling and Merican 1962; and William- 

 son, 1967). Publications on the fresh-water 

 shrimp indigenous to West Africa consist pri- 

 marily of systematic studies. 



A seasonal commercial fishery exists for 

 fresh-water shrimp (known locally as craw- 

 fish), in the lower St. Paul River near Mon- 

 rovia, Liberia, West Africa (fig. 1). In 1952- 

 53, I made a general survey of the fishery and 



