in P. aztecus is more sinuous and slender than 

 in P. duorarum. 



Color. — Juveniles and young adults from 

 estuaries or oceanic water near shore are usually 

 brown or grayish brown, occasionally with darker 

 spots or faint concentrations of chromatophores 

 at the pleural articulations. Individuals from 

 deeper water are light orange (Burkenroad, 1939) . 

 The tail fan is darkened distally and in adults is 

 edged with purple to reddish purple. Detailed 

 coloration of the young has been given by Wil- 

 liams (1953). 



Habitat. — Estuarine and oceanic littoral, pre- 

 dominantly on mud bottom from water's edge 

 to 45 fathoms; rarely to 89 fathoms. 



Type locality. — Veracruz, Mexico. 



Known range. — New Jersey (occasionally to 

 Marthas Vineyard, Mass.) through Gulf of 

 Mexico and West Indies to Uruguay. 



"Form A," New Jersey to Campeche, Mexico. 



"Form B," Florida through West Indies; 

 Panama to Rio de Janeiro, Brazil. 



"Form C," Pernambuco, Brazil, to Montevideo, 

 Uruguay. 



Remarks. — Penaeus aztecus, the third of the 

 littoral penaeids abundant enough to be utilized 

 profitably for food, is also fished commercially 

 throughout much of its range (North Carolina 

 to Brazil), and total landings for this species now 

 outstrip the other two combined. When the U.S. 

 Bureau of Fisheries began research on the natural 

 history of P. setiferus in the 1930's, few grooved 

 shrimp were sold, but with the advent of increased 

 market, larger trawlers, and discovery of large 

 concentrations of both P. duorarum and P. aztecus 

 in different localities than had formerly been 

 fished, the latter species were extensively utilized. 

 Conversely, in recent years it is also possible that 

 there has been a decline in abundance of P. setif- 

 erus throughout much of its range (various 

 authors). Tremendous quantities of P. aztecus 

 are now landed in the western Gulf of Mexico. 



Prior to Burkenroad's revision (1939) of the 

 grooved shrimps of the western Atlantic, three 

 currently recognized species were lumped under 

 the name P. brasiliensis. Biological data taken 

 prior to that time on these species, never so ex- 

 tensive as those for P. setiferus, cannot now be 

 assigned with certainty to any single species. 



However, taking into consideration the locations 

 where research was done, as well as modern 

 knowledge of species distributions, it is probable 

 that most of those data on grooved shrimps apply 

 to P. aztecus (see also Pearson, 1939). 



Maturation of gonads in P. aztecus probably 

 parallels the process as understood in P. setiferus, 

 although few data are recorded on this subject. 

 Broad (1950) described maturing ovaries found 

 in August as opaque white, yellow, tan, or 

 gray in color. Burkenroad (1939), working in 

 Louisiana, noted that whereas the proportion of 

 males to females in P. aztecus near shore was 

 about 1 to 1, this ratio progressively changed in 

 samples farther from shore, in deeper water, to 

 a ratio of 1 to 2 in water 50-70 fathoms deep. 

 Moreover, the females in deep water were much 

 larger than the males, a characteristic shown also 

 by the related P. setiferus and P. duorarum and 

 young adult populations of all three species in- 

 shore. Burkenroad attributed the size disparity 

 of these large offshore individuals to greater 

 length of life among females. Knowledge that 

 impregnated females occurred only beyond 10 

 fathoms, together with the fact that mature (and 

 possibly spent) ovaries <were found only in indi- 

 viduals beyond these depths at various times of 

 year, led him to propose that the females spawned 

 a number of times during an ill-defined spawning 

 season. 



Williams (1959) favorably assessed Pearson's 

 (1939) determination of P. brasiliensis (unfor- 

 tunately misspelled "braziliensis" in Williams) as 

 most probably P. aztecus, and proceeding on the 

 basis of Pearson's distinguishing characters was 

 able to separate P. duorarwm and P. aztecus post- 

 larvae in the plankton in North Carolina. Post- 

 larvae of the latter were found entering the 

 sounds from October to May, with peak recruit- 

 ment from late March to early April. Bearden 

 (1961) found peak recruitment to occur in Febru- 

 ary and March in South Carolina. These patterns 

 agreed well with collections of juveniles (Wil- 

 liams, 1955a) in which recruitment began in 

 mid-April and continued through the summer. 

 A long winter spawning season supplies post- 

 larvae to the Carolina sounds, but fall and mid- 

 winter recruits are apparently killed by cold 

 weather for they never progress beyond postlarvae 



26 



FISH AND WILDLIFE SERVICE 



