Maturity, spermatogenesis and seasonal reproductive cycle of male Rhinobatos annulatus (Muller & Henle, 1841) from Algoa Bay, South Africa, and a novel description for sperm release from the spermatocyst

Abstract

Despite the unique gonadal organization and reproductive strategies known for elasmobranchs very little is known about the reproductive biology of local species. The stages of spermatogenesis for the lesser guitar fish, Rhinobatus annulatus, has not been described and specifically the mechanism for sperm release from the spermatosyst was until now not known. The elongated paired testes, consisting of dome-shaped lobules, were embedded in an epigonal matrix. The lobules consisted of spherical spermatocyst, containing the spermatogenic cells arranged in concentric layers. In each spermatocyst, germ elements were in the same stage of differentiation. Discharging of sperm was found to be conveyed via a ciliated ductule system. The excurrent duct system consisted of the vasa efferentia, epididymis, vas deferens, seminal vesicle and cloaca. Seasonal reproductive activity was evident when the gonadosomatic index reached a maximum in November and a minimum in May. Ripe running males were observed from January to June. Mating took place between April and June. Sexual maturity was reached at a total body length of 580 mm and at three years of age. Knowledge of size/age at sexual maturity and seasonal reproductive activity in the local elasmobranch, Rhinobatus annulatus may prove critical to ensure effective management and conservation strategies for this species.