BIOLOGY OF COMMERCIAL SHRIMPS 



By Milton J. Lindner and William W. Anderson, Fishery Research Biologists, Fish and Wildlife Service 



About 140 million pounds of shrimp were taken 

 from the Gulf of Mexico in 1949. In the Gulf 

 there are four commercially important shrimps: 

 the common, white or lake shrimp, Penaeus 

 setijerus; the grooved, Brazilian, pink and brown 

 shrimp, P. duoarum and P. aztecus; and the sea- 

 bob, Xiphopenaeus kroyeri. Of these, P. setijerus, 

 during the middle 1930's, accounted for about 95 

 percent of the catch. At that time the fishery in 

 the Gulf proper extended from St. Marks, Florida, 

 with gaps, to Brownsville, Texas. Now, the 

 fishery extends along almost the entire perimeter 

 of the Gulf, and P. aztecus and P. duoarum have 

 become progressively more important. Probably 

 more than one-third of the 1949 catch was of these 

 two species. Since we know more about P. 

 setijerus the remarks that follow pertain to this 

 species only and just for the northern Gulf of 

 Mexico. 



P. setijerus is most abuinlant in areas that are 

 characterized by having an inland, brackish marsh 

 connected by passes with an adjacent shallow 

 offshore area of relatively high salinity and mud 

 or clay bottom. The offshore characteristics seem 

 to be required by the adults and probably also the 

 larvae, while the inland marshes appear to be 

 required by the post-larval prc-adults. The 

 adults are rarely found in abundance in the Gulf 

 of Mexico in depths greater than 30 fathoms. 

 The pre-adults inhabit brackish water and at 

 times are found in water that is almost fresh. 



The females do not carry the eggs after fertili- 

 zation but deposit them directly into the water. 

 Some time prior to the emission of the eggs (time 

 not known) the female has a spermatophore 

 attached to her by the male. The eggs upon 

 emission are fertilized by the sperm contained in 

 the spermatophore. A female will lay about 

 500,000 eggs at each spawning, and it is probable 

 that there is more than one spawning in a season. 



As in other peneids, the first larval stage upon 

 hatching from the egg begins as a nauplius. The 



larval stages are represented by at least five 

 naupliar, three protozoeal and two mysis stages. 



Most, if not all, spawning takes place at sea and 

 not in the estuarine inland waters. Either during 

 or shortly after the larval stages the young shrimp 

 move from the waters of the Gulf to the estuarine 

 waters. Growth is rapid in these estuarine waters. 

 WHien the young are about 50 mm. in total length 

 (from tip of rostrum to end of telson) they begin 

 to appear in abundance on the estuarine com- 

 mercial fishing grounds. 



The young first appear in the estuarine fishing 

 grounds in June or July, depending upon the area, 

 and by August they have begun to make their 

 appearance in the waters of the Gulf. Generally, 

 in the estuarine waters there is a gradient in size 

 of the shrimp, smaller shrimp occurring in those 

 waters farther inland and larger shrimp in those 

 waters nearest the Gulf. This gradient in size 

 appears to be associated more closely with locality 

 than with salinity. 



As the young increase in size they gradually 

 move toward the open waters of the Gulf (fig. 70) . 

 The movement of shrimp from the inland waters 

 to the open waters of the Gulf is intensified by the 

 decreasing water temperatures during the fall. 

 As the waters warm in the spring the larger 

 shrimp which are in the open waters of the Gulf 

 mature rapidly and spawn. The smaller shrimp 

 which have wintered in the estuarine waters or 

 in Gulf waters close to shore grow and mature 

 rapidly but spawn later. 



Spawning occurs, and appears to be coa- 

 tinuous, from at least the latter part of March 

 through September. Apparently there are two 

 major peaks of spawning success. The first peak 

 can be attributed to April in Louisiana and 

 generally June near Aransas Pass, Texas. Growth 

 is rapid and the young from these spawnings 

 produce the fall "run" of shrimp. The spring 

 "run" of shrimp is produced by the second peak 

 of spawning success which appears to result from 



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