FISHERY BULLETIN VOL. 77. NO. L' 



of spermatozoa in the oviducal gland could be de- 

 tected using a smear technique as an alternative 

 to the time-consuming process of embedding and 

 sectioning. The oviducal gland was excised with a 

 few centimeters of oviduct attached. The posterior 

 one-third of the gland was removed by cross- 

 sectioning with a clean scalpel. The anterior two- 

 thirds of the gland was then squeezed and the 

 expressed fluid was smeared on a microscope slide. 

 Slides were dried and later fixed and stained with 

 the Harleco Diff-Quik stain system. 



Oviducal glands from 21 sharks were prepared. 

 One from each fish was sectioned; the other gland 

 cut and smeared. Both techniques revealed sper- 

 matozoa in 15 and both methods proved negative 

 for the other 6. The presence of spermatozoa can 

 therefore be determined from fresh smears of the 

 oviducal gland. 



Like Metten (1941), I found varying amounts of 

 spermatozoa in the inseminated glands. Females 

 >200 cm contained relatively few spermatozoa 

 in the tubules. Some fish in the 160-180 cm gi-oup 

 had obviously just copulated, because the tubules 

 of the posterior oviducal gland were distended 

 with sperm (Figure 14) and additional sperm was 

 present in the central lumen. The spermatozoa are 

 stored in the lower lobes of tubules which probably 

 once were shell-secreting in function but now are 

 actively evolving into a seminal receptacle. Since 

 sperm may be stored for over 1 yr and possibly two 

 (see Sexual Cycle below) these tubules must have 

 a mechanism for sperm preservation and nour- 

 ishment. Ducts from the lower lobes also run an- 

 teriorly into the upper ends of the lumen's diver- 

 ticula. 



I suspect that the ova are fertilized at this upper 

 level of the oviducal gland. The exact sequence of 

 events is difficult to understand because of the 

 complex nature of the lumen. 



Sperm Retention in 

 the Female Blue Shark 



Many diverse animals can store spermatozoa for 

 varying lengths of time (Prasad 1944). The pres- 

 ence of spermatozoa in the oviducal glands of 

 pregnant blue shark females would suggest 

 extended storage. Histological examination re- 

 vealed spermatozoa in the oviducal gland of the 

 Sargasso Sea specimen. The other gravid females 

 examined histologically are from northern waters 

 caught in May, June, and July. A total of nine 

 gravid females contained spermatozoa. Two 



females did not contain spermatozoa and it is pos- 

 sible that the glands lacking spermatozoa were 

 poorly fixed, or the spermatozoa was destroyed 

 because these sport-caught fish often hang in the 

 sun for hours before dissection. Alternatively, it is 

 possible that the reservoir of sperm has been 

 naturally depleted and another copulation is 

 necessary. If the female could physiologically 

 sense this depletion, the presence in coastal wa- 

 ters of 225-240 cm nongravid females would be 

 explained. In any case, it may be concluded from 

 the above that spermatozoa can persist in the 

 oviducal gland for at least the length of gestation 

 (9-12 mo). If delayed fertilization is a part of the 

 sexual cycle, then storage for 18-22 mo would be 

 necessary for sperm to be found in a gravid female. 

 Since the oviducal gland is at the anterior end of 

 the uterus it is doubtful that spermatozoa could 

 reach the gland if copulation took place while the 

 female was carrying young. In addition to these 

 physical obstacles to the transfer of spermatozoa, 

 the presence of 110-120 ripe ovarian eggs also 

 suggests that the gravid female is ready for fertili- 

 zation and development of a second litter im- 

 mediately after pupping. The offshore distribution 

 ofmost pregnant females (Aasen 1966; Backus see 

 footnote 7) in areas not frequented by adult males 

 and perhaps unreceptive behavior in the female 

 very likely act to prevent males from copulating 

 with pregnant females. Therefore, it is possible 

 that the quantities of spermatozoa found in the 

 nine gravid female oviducal glands are sufficient 

 for fertilization of the ripe ovarian eggs. 



Sexual Cycle 



The high incidence of mating scars and presence 

 of sperm in the oviducal gland indicate a summer 



1^0 .40 it.0 ISO ..'00 ??0 



BODY FORK LENGTH (cm) 



Fk; 



L'RE 27. — Blue shark sex ratio in June off Bay Shore, Lon^ 

 Island, N.Y., 196.5-72, n = 2,174. 



466 



