pregnation; in the grooved Penaeus this occurs 

 when median borders of lateral plates meet. The 

 minimum length at which I found females with a 

 functional thelycum is 15 mm. c.l., 69 mm. t.l., but 

 in some individuals the lateral plates do not become 

 contiguous until the shrimp attain 20 mm. c.l., 89 

 mm. t.l. Therefore, pink shrimp females attain the 

 subadult stage within the range of 15 to 20 mm. 

 C.L, 69 to 89 mm. t.l. The minimum length at which 

 they have been found with well-developed ovaries 

 is 92 mm. t.l. ; ripe females of this length were re- 

 ported by Eldred et al. ( 1961 ) off Tampa Bay, Fla. 

 This size is larger than that at which females can 

 be first impregnated. 



Eldred (1958) discussed the statement by Bur- 

 kenroad (1939) that the smallest impregnated fe- 

 males of P. duoraritin he found were 23 mm. c.l. 

 and the smallest males with joined petasmal en- 

 dopods were 15 mm. c.l. The smallest impregnated 

 females she had found in Florida waters were con- 

 siderably larger (31 mm. c.l.), and suggested that 

 Burkenroad (who did not mention locality) could 

 have referred to P. dworarum from the Caribbean 

 Sea, that is to say, to P. d. not.ialis. Individuals of 

 the latter subspecies, however, do not seem to at- 

 tain the subadult stage at smaller size than do 

 those of P. d. duorarum. Whatever the locality of 

 Burkenroad's specimens, the discrepancy was 

 caused by a difference in technique — Burkenroad 

 measured the length of the carapace from postor- 

 bital margin to posterior margin of carapace (see 

 Burkenroad, 1936) while Eldred included the ros- 

 trum. Addition of the length of the rostrum to 

 Burkenroad's measurements greatly reduces the 

 discrepancy. 



COPULATION 



Copulation in /-". d. duorarum seems to take place 

 (as in all Penaeus with a complicated thelycum) 

 between a hard-shelled male and a soft-shelled fe- 

 male soon after the female molts. The reasons for 

 this assumption are many: for transfer of the 

 spermatophores into the thelycum the i>etasma 

 must have its two valves firmly joined (soft newly 

 molted males have the petasma unjoined or par- 

 tially joined) ; only hard-shelled males have been 

 seeu with extruding spermatophores; females kept 

 in aquariums were apparently impregnated shortly 

 after molting while in soft-shelled condition, and 

 their exoskeletons carried the spermatophores 

 to the following ecdysis; finally, even in live speci- 

 mens, it is difficult to open the thelycum of hard- 

 shelled females (Eldred, 1958) . 



Copulation takes place several times during the 

 growth and development of the females and is not 

 directly associated with maturation and spawning. 

 This conclusion is based on the facts that sperma- 

 tophores are cast off at each ecdysis and impreg- 

 nated females are found with ovaries in different 

 stages of development, from undeveloped to ripe. 



Impregnated females of P. d. dworarwni carry 

 the spermatophores inside the seminal receptacle 

 and can usually be detected by the strongly convex 

 shape of the lateral plates of the thelyca. The lat- 

 eral jjlates may remain convex after spawning, 

 however, and, thus, their bulging appearance 

 cannot be taken as a certain indication of 

 impregnation. 



There seems to be evidence that offshore P. d. 

 duoranim- mate throughout the year ; in the Tortu- 

 gas area, Ingle et al. (1959) found the largest per- 

 centage of impregnated females in May and June, 

 but also some in all months of the year. 



OVARY DEVELOPMENT 



In P. d. duorarwm, as in all its congeners, the 

 ovaries extend from the anterior end of the cepha- 

 lothorax to the posterior end of the abdomen. 

 Each ovary consists of one anterior lobe and six 

 to eight lateral lobes in the cephalothorax and 

 one long lobe in the abdomen. The size, color, and 

 texture of the ovaries vary with the degree of 

 maturity. The development of the ovary in P. d. 

 diiorarunh has been studied by Cummings (1961), 

 who identified the following stages : 



1. Undeveloped. Ovaries very slender, translu- 

 cent, flaccid, and invisible through the exoskele- 

 ton. Ova transparent, small, modal size less than 

 0.137 mm. 



2. Developing. Ovaries still flaccid, but larger, 

 opaque, white to pale olive-buff'. Modal size of ova 

 0.137 to 0.274 mm. 



3. Nearly ripe. Ovaries larger, relatively light 

 bluish green at the beginning and darker at the 

 end, somewhat turgid, and visible throughout the 

 exoskeleton. Modal size of ova 0.274 to 0.342 mm. 



4. Ripe. Ovaries dark grayish green, very simi- 

 lar in appearance to the previous stage from which 

 they can be distingiiished only microscopically by 

 the presence aroiuid the nucleus of a peripheral 

 layer of rodlike bodies with apices directed toward 

 the center of the ova. According to Ciunmings, the 

 modal size of the ova is slightly less than 0.37 

 mm. Dobkin (1961), however, reported that eggs 

 spawned at the laboratory measured 0.31 to 0.33 

 mm., and Eldred et al. (1965) found that eggs 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



513 



