Sexual development and maturity scale for the angel shark Squatina squatina (Elasmobranchii: Squatinidae), with comments on the adequacy of general maturity scales

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 elasmobranchs 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 development 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 functionality 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.