Vol. 1: 117–132, 2015 SEXUALITY AND EARLY DEVELOPMENT IN AQUATIC ORGANISMS Published online June 11 doi: 10.3354/sedao00012 Sex Early Dev Aquat Org OPENPEN ACCESSCCESS Sexual development and maturity scale for the angel shark Squatina squatina (Elasmobranchii: Squatinidae), with comments on the adequacy of general maturity scales Filip Osaer1,2,3,*, Krupskaya Narváez1,2,3, José G. Pajuelo2, José M. Lorenzo2 1ELASMOCAN, Asociación Canaria para la Investigación y Conservación de los Elasmobranquios, 35001 Las Palmas de Gran Canaria, Spain 2Departamento de Biología, Universidad de Las Palmas de Gran Canaria, Edificio de Ciencias Básicas, Campus de Tafira, 35017 Las Palmas de Gran Canaria, Spain 3Fundación Colombiana para la Investigación y Conservación de Tiburones y Rayas, SQUALUS, Carrera 60A No 11−39, Cali, Colombia ABSTRACT: This paper contributes to the reproductive biology of the genus Squatina and aims to complement the criteria, uniformity and adaptable staging of sexual maturity scales for elasmo- branchs based on data from the angel shark S. squatina captured near the island of Gran Canaria (Canary Islands, Central-East Atlantic). Both sexes presented a paired reproductive tract with both sides active and asymmetric gonad development. Microscopic and macroscopic observations of the testes were consistent and indicated seasonality of spermatogenesis. The spermatocyst de - velopment pattern in mature individuals could not be assigned to any of the categories described in the literature. The ovaries−epigonal organ association was of the external type. Although all Squatinidae share a conservative morphology, they show differences across species in the func- tionality of the paired reproductive tract, seasonality of spermatogenesis, coiled spermatozoa and the presence of egg candles. A flexible classification technique was used to describe an illustrated 5-stage sexual maturity scale using an ontogenic approach, assessable by macroscopic condition indices. The phases include juvenile, subadult, developing, active/pregnant and spent/post-partum in males and females, respectively. Claspers were considered calcified when it was necessary to break a clasper when bending the axial cartilage 180° over its longitudinal axis. Recent general maturity scale proposals for elasmobranchs could not be adapted. The interspecific variations in fish development, which do not facilitate a standard terminology across all fishes, indicate the need for species-specific and adaptable macroscopic and microscopic staging schema, rather than using generalized classification systems. KEY WORDS: Reproductive biology · Elasmobranch · Macroscopic analysis · Histology · Viviparous · Lecithotrophy · Seasonality · Canary Islands INTRODUCTION history characteristics and bycatch in fisheries with steadily increasing effort and capacity, its abundance The angel shark Squatina squatina, which has a has dramatically declined during the past 50 yr lecithotrophic viviparous reproduction mode (Budker (Morey et al. 2006). The species is considered extinct 1958, Capapé et al. 1990), is a bottom-dwelling spe- in the North Sea (ICES 2005, 2014) and Critically cies of the European and North African continental Endangered in its remaining range, with the possible shelves (Ebert & Stehmann 2013). Because of its life exception of some areas of the southern Mediterran- © The authors 2015. Open Access under Creative Commons by *Corresponding author: [email protected] Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 118 Sex Early Dev Aquat Org 1: 117–132, 2015 ean and the Canary Islands, where its status must be reproductive tract with 2 immature and mature confirmed and conservation measures should be phases for males. Similarly, for females, 2 immature introduced as a matter of urgency (Morey et al. 2006, phases were described, and 4 and 5 phases based on ICES 2014). Despite concerns regarding the conser- either the ovarian or uterine activity for oviparous vation status of this species, limited information is and viviparous species, respectively. Walker (2005) available about its life history parameters. For exam- introduced condition indices of different organs from ple, the only study on the reproductive biology of S. the reproductive tract with a key for immature or squatina was by Capapé et al. (1990) along the mature phase assumption only. Brown-Peterson et al. Tunisian coast. (2011) highlighted the need for unified terminology Investigating chondrichthyan population dynamics and described a conceptual model for reproductive requires detailed information regarding the repro- development and a maturity scale with a correspon- ductive biology of a species, including clear defini- ding terminology for all fishes that was based on tions for distinguishing between maturity phases, micro- and macroscopic observations from teleosts. timing of ovulation and periodicity of gestation and However, reviews on fish reproduction have re- parturition (Walker 2005). Precise and clear descrip- vealed inconsistencies in this proposal, especially re - tions, including pictures, of the main characteristics garding the definition of an ovarian follicle. Addi- of gonads in different stages are required to min- tionally, interspecific variations in fish oocyte devel- imise mistakes in the assignment of maturity stages opment do not lend themselves to a standard termi- for the correct calculation of maturity ogives (ICES nology across all fishes. Therefore, a staging schema 2007). This level of detail is lacking for most elasmo- for oocyte development needs to be adaptable to spe- branch species and for all species in the genus cies’ variations (Grier 2012). The most recent propos- Squatina. Additionally, the maturity assessment cri- als of general maturity scales for elasmobranchs, viz. teria have not been consistent among the different ICES (2010, 2013), and the studies from the repro- studies of the genus. Most works considered a juve- ductive biology of a viviparous and oviparous elas- nile, subadult and mature phase in males and mobranch species of Paiva et al. (2011) and Serra- females based on the length and calcification of the Pereira et al. (2011), respectively, affirmed having clasper and on the condition of the ovaries, oviduct consistently adopted the proposed terminology of and oviducal gland, following Capapé et al. (1990) Brown-Peterson et al. (2011). Despite this, all men- (Bridge et al. 1998, Capapé et al. 2002, 2005, Co lo - tioned studies showed differences with the concep- nello et al. 2007). Other research only included a tual model and terminology proposed by Brown- mature and an immature phase following the former Peterson et al. (2011). To this end, the specific objec- criteria (Awruch et al. 2008) or with the distinction of tives of the current study were to (1) establish a com- an actively reproducing stage based on the condition prehensive and illustrated maturity scale that is of the epididymides and ova and uteri (Shelmerdine based on unambiguous condition indices from & Cliff 2006), as well as sperm smears (Natanson & macro scopic observations and that is based on stan- Cailliet 1986). In contrast, Baremore (2010) based dardised methods for elasmobranch reproduction maturity determination on conditions described by studies, (2) confirm the macroscopic testes observa- Walker (2005) and on secondary characteristics and tions using histology and (3) compare the spermato- arbitrary size criteria for follicles and for nidamental cyst development pattern with the described cate- glands, respectively. The study by Natanson & Cail- gories in the literature. liet (1986) is the only study that considered 5 maturity phases in females: juvenile, subadult, mature, repro- ductively active and post-partum based on the condi- MATERIALS AND METHODS tion of the ovaries, the size of the follicles and ovi - ducts and the number of ova or embryos. However, Angel sharks were collected from incidental cap- the size range of follicles between 10 and 50 mm is tures from the coastal artisanal fishery on the island not covered in the description. of Gran Canaria (Canary Islands) between 2007 and The importance and the need to standardise crite- 2009. During the sampling, the presence of fluids in ria used to assess elasmobranch reproductive devel- the seminal vesicles and the clasper glands was opment and to maintain a level of consistency be - recorded. Fluids were analysed for fertility under a tween studies has been noted in recent years (Steh - stereoscopic microscope. All specimens were then mann 2002, Walker 2005). Stehmann (2002) de - deep-frozen for later analysis in the laboratory. The scribed maturity phases based on descriptions of the thawing process was controlled over approximately Osaer et al.: Sexual maturity scale for Squatina squatina 119 12 h by insulating the individuals. Bio - metric measurements were taken to the nearest mm: the total length from the tip of Spent Spent the snout to the ventral tip of the caudal fin, the diameter of follicles containing vitellogenic oocytes, and the maximum length and width of the testes− epigonal organ com plex (TE), ovaries− epigonal or- III, Developing; gan com plex (OE) and uteri. The condition of the reproductive tract was recorded based on macroscopic observations. These 180° over its longitudinal axis re sults were then assigned to condition classes that were modified from Walker guish maturity