196 MARINE FISHERIES OF NORTH CAROLINA 



sery conditions) in P. brasiliensis. P. duorarum seems more adaptable to 

 salinity differences than the other shrimps. 



Shrimp are warm-water forms. Weymouth, Lindner, and Anderson (1933) 

 list the limits of temperature within which P. setijerus is taken as 9° to 31° C. 

 (48° to 88° F.). Burkenroad (1939) suggests that temperature higher than 

 20° C. (68° F.) during some time of the year may be necessary for the 

 maintenance of the various species. 



NATURAL HISTORY 



LARVAL DEVELOPMENT 



In studies of shrimp, as in studies of most animals which contribute to 

 the world's fisheries, too little attention has been given to the developmental 

 stages. Yet the success with which the various larval stages meet is the 

 prime determinant of the fishery. Each stage in the life history is as im- 

 portant as the adult, for each must be passed by each generation. Shrimp 

 do not hatch from eggs as miniature adults, nor do the habits of these larval 

 stages resemble those of mature shrimp. Thus, knowledge of the larvae 

 (their food, habitat, natural enemies, tolerances, and tropisms) is as much 

 a part of the natural history of the various species as is an understanding 

 of the adult animals. 



Published information on shrimp larvae is, however, limited. Of our 

 Atlantic species, the development of P. setijerus has been described (Pear- 

 son, 1939), but there is no account of the larvae of our other species of 

 Penaeus. Since the various commercial shrimps are closely related, similarity 

 may be expected in their larval histories. At the same time, the differences 

 in morphology, behavior, and distribution of the adults should have their 

 counterparts in the larvae. The lack of information regarding shrimp larvae 

 is, therefore, a serious deficiency in our understanding of the natural his- 

 tories of the various species. 



Of P. setijerus, Pearson (1939) reports ten distinct stages, falling into 

 three general headings, between the egg and the post-larva or subadult. 

 The eggs are found only at sea, and the ten larval stages live as plankton 

 or floating small-life in the open ocean. 



Shrimp belonging to the family Penaeidae, do not carry the eggs about 

 as do most crustaceans, but lay them directly on the bottom where they 

 are left to hatch. The eggs of P. setijerus are about 0.28 mm. (1/90 inch) in 

 diameter and are described by Pearson as having a "characteristic purplish- 

 blue" color. They are demersal (that is, they sink) in sea water. A female 

 may lay as many as half a million eggs in a single spawning. "Nearly all" of 

 the eggs found by Pearson were in late developmental stages. Of those that 

 hatched, all did so within twelve hours. 



