viduals up to 22 mm. c.l., 97 mm. t.l., may have the 

 petasma unjoined. Thus, males seem to attam the 

 subadult stage at a carapace length of 19 to 23 nam., 

 or 85 to 101 mm. t.l. It is possible, however, that 

 some males attain this stage at a smaller size. 



The smaller females I foimd to have reached 

 the subadult stage were 18 mm. c.l., 82 mm., t.l. 

 Individuals up to 22 mm. c.l., 97 mm. t.l., however, 

 may have the thelycum with lateral plates non- 

 contiguous; thus, the subadult stage is attained be- 

 tween 18 and 23 nma. c.l., 82 to 101 mm. t.l. 



Burkenroad (1939) reported that female brown 

 shrimp reach sexual maturity or gonadal ripeness 

 at about 30 mm. c.l. or about 14.5 nun. t.l., and 

 Renfro (196-1) found that sexual maturity is usu- 

 ally first, attained at a total length of about 140 

 mm. 



COPULATION 



Burkenroad (1939) was the first, to suggest that 

 copulation in P. a. aztecus takes place between a 

 soft-shelled female and a hard-shelled male, as is 

 now thought to be true for all Penaeiis with a 

 closed thelycum. Copulation occurs without re- 

 spect to the developmental stage of the ovaries. 



Impregnated females can usually be detected 

 macroscopically, like those of the other Penaeus 

 with a closed thelycum, by the Inilging of the lat- 

 eral plates and the tumid appearance — the "lip"' 

 of their borders. These criteria are not infallible 

 however, because the lateral plates remain strongly 

 convex in recently spent females. 

 OVARY DEVELOPMENT 



Like many of its congeners, P. a. aztecus 

 possesses ovaries consisting of one anterior lobe 

 from which project six to eight lateral lobules 

 and one {wsterior lobe that extends to the base 

 of the telson. The size, color, and texture of tlie 

 ovaries change with the degree of maturity. 



Burkenroad (1939) distinguished three stages 

 in the development of the ovary, which correspond 

 approximately to the last three stages recognized 

 by Cummings (1961) in P. d. duoramm. Five 

 stages of ovarian development are now generally 

 accepted. 



1. Undeveloped. Ovaries slender, flaccid, and 

 translucent. Ova small and translucent. 



2. Developing. Ovaries opaque, yellowish with 

 numerous heavily granular ova; diameter of ova 

 0.10 to 0.18 mm. 



3. Nearly ripe. Ovaries large, yellowish brown. 



becoming darker bi'own. Diameter of ova 0.19 to 

 0.25 mm. 



4. Eipe. Ovaries golden brown. Diameter of 

 ova 0.26 to 0.28 mm. 



5. Spent. Ovaries greatly reduced in diameter, 

 flaccid, light brown to yellowish. 



SPAWNING 



The information on spawning — depths, seasons, 

 and peaks — of brown shrimp has been largely de- 

 duced from records of the occurrence of females 

 with ripe or spent ovaries and the distribution 

 and abundance of larvae and postlarvae. P. a. az- 

 tecus spawns at sea, usually in water deeper than 

 10 fm. and down to at least 60 fm. (Eenfro and 

 Brusher, 1965). Laboratory experiments by Cook 

 (1965) indicated that spawning takes place at 

 night. Spawning activity varies through the range 

 of the shrimp and with depth. According to studies 

 on ovary development by Renfro and Brusher 

 ( 1965) in the northwestern Gulf of Mexico, spawn- 

 ing is continuous in depth between 25 and 60 fm. 

 and appears to be most intensive during the fall. 

 At 15 fm., however, spawning is restricted, taking 

 place, from March-April through November-De- 

 cember, and maximum spawnmg activity appar- 

 ently occurs in late summer. Recently, Temple and 

 Fischer (1967) indicated from the seasonal abun- 

 dance of larvae that the maximum peak of 

 spawning was from September to Noveml>er. Stud- 

 ies on abundance of juveniles (Gunter, 1950) and 

 those on population dynamics, including general 

 knowledge of maximum aggregations of postlan'ae 

 in the nursery grounds (Kutkulm, 1962) indicated 

 that two annual peaks of spawning occur in the 

 northern Gulf of Mexico, one in early spring and 

 the other in the fall. 



Along the southeastern Atlantic Coast of the 

 United States a single peak of spawning activity 

 seems to occur in February or March (Williams, 

 1956a, 1959 ; Bearden, 1961 ; Joyce, 1965) . In North 

 Carolina, Williams" (1965) collection of post- 

 larvae in the sounds from October to May indi- 

 cates a protracted spawning season including fall 

 and winter, but the postlarvae that reach inshore 

 waters are apparently killed by low temperatures 

 because no juveniles were found until mid-April. 

 In the northern Gulf of Mexico and the south- 

 eastern Atlantic Coast of the United States, the 

 first peak of brown shrimp spawning occurs 

 earlier in the year than do those of P. setiferus 

 and P. d. duorarum; the postlarvae of the latter 

 do not appear until May or June, after those of 



540 



U.S. FISH AND WILDLIFE SERVICE 



