Histological Observation of the Urogenital Papillae in the Bi-Directional Sex-Changing Gobiid Fish,Trimma okinawae

Abstract

The gobiid fish Trimma okinawae changes its sex bi-directionally according to its social status. Morphological changes in the urinogenital papillae (UGP) of this fish have been reported during sex change. However, there have been no detailed observations of such changes. Here, we histologically examined the UGP structure of male- and female-phase fish. UGPs of fish in female and male phase contained both oviducts and sperm ducts. Both ducts were coalesced into one duct within the posterior region of the UGP. Female-phase fish had many longitudinal folds in the hypertrophied tunica mucosa of the oviduct, which was found to be responsible for the transport of eggs and the removal of follicular cells from the oocyte. In contrast, male-phase fish had an immature oviduct and a mature sperm duct in the UGP. In the male-phase fish, the co-existence of spermatozoa and fibrillar secretions was observed in the sperm duct during spermiation.

Morphology of the urogenital papilla and its component ducts in Astyanax altiparanae Garutti & Britski, 2000 (Characiformes: Characidae)

“…Similarities in this structure can be found among evolutionarily distinct groups, such as the Neoteleostei bluehead wrasse Thalassoma bifasciatum (Bloch, 1791) (Labriniformes) and the Euteleostei chum salmon Onchorhynkus keta (Walbaum, 1792) (Salmoniforms), whose divergence time was more than 290 million years ago and both of them show the genital and urinary ducts opening independently on the papillary surface (Uematsu & Hibiya, 1983;Ross, 1984;Hastings & Petersen, 1986;Rasotto & Shapiro, 1998;Ortí & Li, 2009;Kobayashi et al, 2012).…”

“…For example, the lamellae formation by the oviduct epithelium may be related to oocyte transportation to the urogenital opening (Kobayashi et al, 2012). This mechanism would be similar to the peristaltic movements of the uterine tube in mammals.…”

“…This mechanism would be similar to the peristaltic movements of the uterine tube in mammals. By contrast, the sperm duct epithelium is related to seminal f luid production (Kobayashi et al, 2012;Spadella et al, 2012), and according to Lahnsteiner et al (1998), feeds the spermatozoa and keeps them motionless.…”

“…Most studies only describe its macroscopic morphology and anatomical position for use identifying the sex of individuals, in fish farming and for toxicological and ecological studies (Ferreira et al, 2010;Kruger et al, 2013). Moreover, most past histological studies were focused on marine fish species (Ross, 1984;Hastings & Petersen, 1986;Kott et al, 1988;Rasotto & Shapiro, 1998;Suzuki & Shibata, 2004;Kobayashi et al, 2012).…”

External reproductive structures of male Surfperches (Embiotocidae): Urogenital papilla

“…Our anatomical findings are similar to the histological observations and descriptions of the urogenital papillae in other teleost species. Additionally, the term urogenital papillae has been described as the external opening with both excretory and reproductive structures in several species, for example, the California grunion ( Leuresthes tenuis ; Aryafar et al, 2019), bluehead wrasse (Rasotto & Shapiro, 1998), the gobiid fish ( Trimma okinawae ; Kobayashi et al, 2012), the serranid fish ( Serranus fasciatus ; Hastings & Petersen, 2004), freshwater tetra ( Astyanax altiparanae ; Siqueira‐Silva et al, 2015), and chum salmon ( Oncorhynchus keta ; Uematsu & Hibiya, 1983). We recognize that these histological studies have focused on externally fertilizing species; however, there is little research focused on the papillae of internally fertilizing, marine fishes.…”