Abstract
Elasmobranchs are facing a global conservation crisis due to human activities.1 The Mediterranean Sea is significantly affected, and predictions show that in the near future, its vulnerable ecosystems will be even more impacted.2,3 Complete knowledge of elasmobranch reproductive biology is essential to establish assisted reproductive protocols for their future application in ex situ or in situ endangered species conservation projects. Despite being one of the most abundant shark species in the Spanish Mediterranean coast,4,5 small-spotted catshark (Scyliorhinus canicula) populations are sensitive to overexploitation and pollution6. S. canicula is a small, easy-to-handle shark, commonly housed in aquaria. For these reasons, this elasmobranch species was chosen as a reproductive model. This study aimed to determine the differences in semen parameters between wild and aquarium-housed animals. Total volume, sperm concentration, motility, viability, mitochondrial activity, membrane integrity, and morphometry, were assessed for each semen sample. These parameters were evaluated as previously described for others elasmobranch species.7,8 A total of 20 semen samples were used (10 from wild animals and 10 from aquarium-housed animals). Volume, concentration, and morphometry data are expressed as the mean ± standard deviation (SD) and motility, viability, mitochondrial activity, and membrane integrity were expressed as the mean ± standard error (SE). The results showed that semen volume was significantly lower in aquarium-housed sharks than in its wild counterparts (0.9±0.2 vs. 2.1±1.1 mL, p<0.05). Similar results between both groups were found in sperm concentration (80.8±38.4 vs. 98.4±43.3×106 spermatozoa/mL for aquarium and wild samples respectively, p=0.174) but differences were found in total sperm count (69.4±34.6 vs. 221.8±201.9×106 spermatozoa per sample, for aquarium and wild samples, respectively, p<0.05). Total sperm motility was significantly higher in semen samples collected at aquarium (57.7±6.6 vs. 24.7±6.1%, for aquarium and wild samples, respectively, p<0.05). However, the samples in the wild and the aquarium group did not differ significantly (p=0.650) with respect to sperm viability (80.0±4.2 vs. 82.1±4.7%), mitochondrial activity (96.8±0.8 vs. 95.5±1.3%, p=0.369), and membrane integrity analysis (72.8±3.6 vs. 71.5±6.3%, p=0.841). Moreover, significant differences were found between groups regarding sperm morphometry for aquarium and wild samples in acrosome (2.8±0.5 vs. 3.0±0.3 μm, p<0.05) and head lengths (41.0±1.1 vs. 41.8±1.3 μm, p<0.05) but no differences were found in midpiece length (18.2±1.0 vs. 18.3±1.1 μm, p=0.566). In conclusion, a significant reduction in the sperm motility was observed in wild animals compared to those obtained in the aquarium. This reduction may be due to the time elapsed between the wild animals capture and the sample retrieval. Differences in acrosome and head does not seem to affect overall sperm quality based on the studied parameters. Beyond that, this study demonstrated that S. canicula in aquaria have quite similar sperm quality than wild ones; thus, it could be considered a model for developing assisted reproductive technologies, but further studies are needed to confirm that assumption.
Acknowledgement
The authors would like to thank the Oceanogràfic and Fundación Oceanogràfic staff, local fishermen, and Pablo García for the support during sample collection.
*Presenting author
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