Sulikowski et al.. The reproductive cycle of Amblyra/a rodiata 



537 



creasing commercial importance, declines in biomass 

 levels, and a paucity of specific biological information, 

 commercial harvests of thorny skates in the U.S. por- 

 tion of the western North Atlantic are now prohibited. 

 Thus, obtaining life history information for this skate 

 species is not only timely (Simpfendorfer, 1993; Frisk et 

 al., 2001), but it has become imperative. The objective of 

 the present study was to describe the patterns of sev- 

 eral morphological reproductive parameters manifested 

 during the reproductive cycle of female and male A. 

 racliata collected in the western Gulf of Maine. 



Materials and methods 



cysts in the testes of 25% or greater were considered 

 reproductively capable of fertilizing an ovulated follicle. 

 These criteria are consistent with previous studies that 

 reported similar characteristics for other mature elas- 

 mobranch species (Koob et al., 1986; Heupel et al., 1999; 

 Conrath et al., 2002; Sulikowski et al., 2004). Male and 

 female thorny skates that did not meet all the criteria 

 were considered to be immature. We also looked for 

 some other indicators of reproductive activity, such as 

 mating bites on female pectoral fins, and evidence of 

 mating activity on male claspers, but they were either 

 absent or not apparent in specimens examined during 

 the study. Sperm storage was not assessed in the pres- 

 ent investigation. 



Sampling 



Thorny skates were captured by otter trawl in an area 

 approximately 900 square miles centered at 42°50'N and 

 70°15'W in the Gulf of Maine. These locations varied 

 from 30 to 40 km off the coast of New Hampshire. Col- 

 lection of skates occurred between the 10 th and 20 th 

 of each month beginning May 2001 and ending May 

 2003. A comparison of samples taken from the same 

 month between different years revealed no variability. 

 Furthermore, the skates sampled in the present study 

 were obtained from the same population and geographic 

 location. Thus, the data from the same months for dif- 

 ferent sampling years were grouped together. 



Skates were maintained alive on board the FV Mys- 

 tique Lady until transport to the University of New 

 Hampshire's Coastal Marine Laboratory (CML). There, 

 individual fish were euthanized (0.3 g/L bath of MS222). 

 Total length (TL in mm) was measured as a straight 

 line distance from the tip of the rostrum to the end 

 of the tail, and disc width (DW in mm) as a straight 

 line distance between the tips of the widest portion of 

 pectoral fins. Total wet weight (kg) was also recorded. 

 For males, clasper length was measured as the straight 

 line distance from the posterior point of the cloaca to 

 the end of the clasper. The gonadosomatic index (GSI) 

 and hepatosomatic index (HSI) were calculated as gonad 

 weight divided by total body weight multiplied by 100, 

 and liver weight divided by total body weight multiplied 

 by 100, respectively. The epigonal organ was included 

 in both male and female GSI measurements because of 

 its close association with the gonads (Maruska et al., 

 1996). 



Criteria used to determine reproductively active skates 



Females whose reproductive tracts contained ovarian 

 follicles with a minimum diameter of 25 mm and had 

 a shell gland weighing at least 30 g were considered 

 mature (capable of egg encapsulation and oviposition). 

 These numbers were determined from our observations 

 of reproductive tracts containing egg cases that were 

 either fully formed or undergoing various stages of 

 formation. Males with calcified claspers 200 mm long 

 or greater, and with a proportion of mature spermato- 



Gross morphology of the female reproductive tract 



After removal of reproductive tracts, the ovaries, shell 

 glands, and uteri were dissected out, blotted dry, and 

 weighed to the nearest gram. Ovarian follicle dynamics 

 were evaluated by measuring the diameter (with a cali- 

 per) and counting all follicles al mm in diameter (Tsang 

 and Callard, 1987; Snelson et al., 1988; Sulikowski et 

 al., 2004). For this data set, we averaged the size of the 

 largest single follicle found on the right and left ovaries 

 of each skate. Average follicle diameters, average ovary 

 weights, and average shell gland weights were analyzed 

 to assess temporal patterns during the reproductive 

 cycle. 



Histology of the testis 



From male specimens, testes were removed, blotted 

 dry, and weighed to the nearest gram. A single 2-3 mm 

 thick segment was removed from the central portion of 

 a single lobe in the medial area of an individual testis 

 (Maruska et al., 1996; Sulikowski et al., 2004), placed 

 in a tissue cassette, and fixed in 10% buffered formalin 

 until processed by the University of New Hampshire 

 Veterinary Diagnostic Laboratory. There, the sample 

 was dehydrated, embedded in paraffin, sectioned, and 

 stained with hematoxylin and eosin. Prepared slides 

 of testicular tissue were examined and classified into 

 stages of spermatogenic development following the cri- 

 teria described by Maruska et al. (1996), Hamlett and 

 Koob (1999), and Tricas et al. (2000). For the develop- 

 mental stages of spermatogenesis described in other 

 elasmobranchs, hormone analyses have confirmed that 

 stages III through VI are associated with reproduc- 

 tive readiness (Heupel et al., 1999; Tricas et al. 2000; 

 Sulikowski et al. 2004). For this reason, we focused 

 our efforts on these specific stages in the thorny skate. 

 Briefly, these stages have the following characteristics: 

 stage III, spermatocysts; stage IV, spermatids; stage 

 V, immature spermatozoa; and stage VI, mature sper- 

 matocysts (Maruska et al., 1996). In the present study, 

 the mean proportion of testis occupied by each of these 

 stages was measured along a straight line distance 

 across one representative full lobe cross section of the 

 testis (Maruska et al., 1996; Conrath et al., 2002). 



