Morphology of the urogenital papilla of the male marine teleost Black Rockfish, Sebastes schlegelii (Hilgendorf, 1880), and its role in internal fertilization

Abstract

There are few detailed descriptions of the morphology of the male external genitalia, the urogenital papilla (UGP), of the Black Rockfish (Sebastes schlegelii Hilgendorf, 1880). The purpose of this study was to evaluate this organ histologically and to determine the time of development of the UGP in Black Rockfish. Twelve adult males, three adult females and around 500 juveniles were used in the experiment.The juveniles were divided into normal developmental and androgen groups. The androgen group was exposed to methyltestosterone (100 μg/L) for 2 h daily for 38 days. Samples (N = 10 per sampling) were randomly selected for analysis every 5 days from 30 to 116 days after birth. Parameters assessed included the type of epithelium, composition of connective tissue, muscular tissue, and the timing of UGP development. Differences in these parameters between normal developmental and androgen groups were evaluated. The results indicated that the UGP of the adult fish contains the sperm duct and ureter, which have the function of transporting sperm and urine, respectively. The androgen-treated juvenile fish developed the UGP earlier than the normal development group. This study provides a reference for understanding the external genitalia of other viviparous fishes by studying the UGP of the male Black Rockfish.

Developmental regulation of the male urogenital papilla in the male marine teleost black rockfish, Sebastes schlegelii (Hilgendorf, 1880)

“…The testes of male black rockfish initiate development in September each year, with functional sexual maturation and mating generally occurring in November; black rockfish sperm ducts were found to contain large numbers of sperm in November [8]. In November, males deliver sperm to the females.…”

“…Expression and function of ara, arb, mafb, and shha in the UGP of juvenile fish Expression of key genes (ara, arb, mafb, shha) in normally developing juvenile black rockfish almost always begins to rise around 40 DAB, probably because gonadal differentiation begins around 40∼50 DAB in black rockfish [8,40]. The ar localization signal is strongest around 60 DAB, a period of testicular differentiation, probably as a result of an increase in the number of proliferating undifferentiated fibroblasts, a stage that is important for UGP organ remodeling.…”

“…Expression of androgenic phenotypes is regulated by steroid hormones, particularly androgens, such as testosterone, dihydrotestosterone, methyltestosterone, and 11-ketotestosterone [8, 9]. The physiological functions of androgens are mediated through androgen receptors (ARs).…”

“…The black rockfish ( Sebastes schlegelii ) belongs to the family Scorpaenidae in the order Scorpaeniformes; as viviparous fish, it is easy to distinguish between males and females after sexual maturity [24]. The external genitalia of adult male black rockfish consist of conical, fleshy papillae called urogenital papilla (UGP) [8]. The UGP contains the sperm duct and ureter, which have the function of transporting sperm and urine, respectively [8, 24].…”

“…The external genitalia of adult male black rockfish consist of conical, fleshy papillae called urogenital papilla (UGP) [8]. The UGP contains the sperm duct and ureter, which have the function of transporting sperm and urine, respectively [8, 24]. Previous research has explored the regulation of external genital development in mammals [13, 23, 25]; however, the involvement of the ar gene in the masculinization of fish external genitalia remains uncertain.…”