Comparative Study of Semen Parameters and Hormone Profile in Small-Spotted Catshark (Scyliorhinus canicula): Aquarium-Housed vs. Wild-Captured

Abstract

Several chondrichthyan species are threatened, and we must increase our knowledge of their reproductive biology in order to establish assisted reproductive protocols for ex situ or in situ endangered species. The small-spotted catshark (Scyliorhinus canicula) is one of the most abundant shark species of the Mediterranean coast and is easy to maintain in aquaria; therefore, it is considered an ideal reproductive model. This study aimed to compare S. canicula male reproductive function in aquarium-housed (n = 7) and wild-captured animals, recently dead (n = 17). Aquarium-housed animals had lower semen volume (p = 0.005) and total sperm number (p = 0.006) than wild-captured animals, but similar sperm concentrations. In terms of sperm parameters, aquarium-housed sharks showed higher total sperm motility (p = 0.004), but no differences were observed regarding sperm viability, mitochondrial membrane potential, or membrane integrity. A morphometric study pointed to a significantly longer head (p = 0.005) and acrosome (p = 0.001) in wild-captured animals. The results of the spermatozoa morphological study of S. canicula were consistent with previous results obtained in other chondrichthyan species. With regard to sex hormones, testosterone levels were significantly lower in aquarium-housed animals (p ≤ 0.001), while similar levels of 17β-estradiol and progesterone were found. In short, the present study provides evidence of good in vitro semen quality in S. canicula housed in an aquarium, underlining their excellent potential for application in reproductive technologies for this and other chondrichthyan species.

Keywords: Elasmobranchii; Scyliorhinidae; conservation biology; sperm; spotted dogfish.

Figure 1

Geographical locations of aquarium and fisheries for the small-spotted catshark (Scyliorhinus canicula) used in this study. Maps of Europe, Spain, and Valencia (area inside the square). Black dots indicate the sample collection points. (A) Oceanogràfic de Valencia (aquarium-housed animals); (B–D) Valencia (39°26′45″ N, 0°19′12″ W), Cullera (39°09′58″ N, 0°15′10″ W), and Jávea Ports (38°47′21″ N 0°09′47″ E), respectively (wild-captured animals during fishing). The gray diamond indicates the Valencia buoy, (39°52′ N, 0°20′ E) used to monitor water parameters related to wild-captured animals (www.puertos.es/es-es/oceanografia/Paginas/portus.aspx, accessed 12 April 2020).

Figure 2

Representative images of small-spotted catshark (Scyliorhinus canicula) sperm cell quality. Scale bar, 20 μm. (A) Epifluorescence micrographs of sperm cells stained with SYBR-14 (green) and propidium iodide (red) at 200× magnification. Green fluorescence shows live sperm, and red fluorescent indicates dead sperm. (B) Epifluorescence micrographs of sperm cells stained with JC-1 at 200× magnification. The dye changes emission wavelength depending on membrane potential by a shift from orange, showing high potential (square), to green color, showing low potential (asterisk). (C) Phase-contrast image displaying tail swelling to assess the functional integrity of membrane by hypoosmotic swelling test at 200× magnification. Coiled tail spermatozoa were identified as having a functional intact plasma membrane (triangle); normal tail spermatozoa were identified as having a nonfunctional intact plasma membrane (octothorpe).

Figure 3

A representative image of ultrastructure of small-spotted catshark (Scyliorhinus canicula) sperm cells. Scanning and transmission electron micrographs of longitudinal and transverse sections through the main pieces of the spermatozoon. The top pictures were obtained with transmission electron microscopy, while the bottom pictures were obtained with scanning electron microscopy. The spermatozoa designed parts are labeled as follows: aac, accessory axonemal column; am, axial rod of midpiece; ax, axoneme; bnf, basal nuclear fossa; bsl, persistent base of cytoplasmic sleeve; cc, cytoplasmic canal; cs, cytoplasmic sleeve; dc, distal centriole; gg, glycogen granules; m, mitochondrion; ms, fibrous sheath of midpiece; n, nucleus; pa, parachromatin.

Figure 4

Box plot comparing blood hormonal sexual values between aquarium-housed and wild-captured small-spotted catshark (Scyliorhinus canicula).