Microanatomy of the female reproductive system of the viviparous freshwater whipray Fluvitrygon signifer (Chondrichthyes: Myliobatiformes: Dasyatidae). II. The genital duct

Nittaya Somsap,Kannika Chatchavalvanich,Nopparat Srakaew

doi:10.1186/s40850-021-00070-0

Abstract

BackgroundFundamental knowledge on microscopic structures of the whole female chondrichthyan genital ducts from a single species remains unavailable. The present study describes microanatomy of the entire female genital duct (anterior oviduct, oviducal gland, uterus and vagina) of the freshwater dasyatid Fluvitrygon signifer.ResultsThe females have only the left genital duct. The genital ducts reveal histological variation among individuals in terms of tissue organization, histochemical profiles and secretory activities. The anterior oviducts of mature females possess branched mucosal folds and exhibit dynamic relationship between production and secretion of secretory substances, while those of immature/regenerating females have short, unbranched mucosal folds and inactive secretory activities. The oviducal gland comprises glandular tubules, which show histological and histochemical heterogeneity and, thus, can be classified into three types. The uterus is categorized into five patterns principally based on histological features of the trophonematal and uterine mucosa. The vagina displays different histochemical reactions, likely reflecting various degrees of glycosylation of secretory granules.ConclusionsThe genital ducts of the females of F. signifer show differential microscopic and histochemical characteristics, indicating their different reproductive statuses.

Highlights

Fundamental knowledge on microscopic structures of the whole female chondrichthyan genital ducts from a single species remains unavailable
This study aimed to investigate the microanatomy of the genital ducts of the freshwater dasyatid, Fluvitrygon signifer
The females have only the left genital duct that is divided into four regions from the anterior to the posterior direction: the anterior oviduct, the oviducal gland, the uterus and the vagina

Summary

Introduction

Fundamental knowledge on microscopic structures of the whole female chondrichthyan genital ducts from a single species remains unavailable. The present study describes microanatomy of the entire female genital duct (anterior oviduct, oviducal gland, uterus and vagina) of the freshwater dasyatid Fluvitrygon signifer. The female reproductive system of the Chondrichthyes generally comprises the ovaries and the genital ducts. The latter are further subdivided into distinct functional regions, namely the ostium, anterior oviduct, oviducal gland, isthmus and uterus [1,2,3]. It is rare and threatened according to IUCN [27] This dasyatid stingray mainly inhabits the freshwater ecosystems of the Indo-Malay Archipelago, with their first record in the Kapuas (Kalimantan, Indonesia) and subsequently in Indragiri river (Riau, Sumatra, Indonesia), the Perak river (western Peninsular Malaysia), Chao Phraya river (Thailand) [28], and Musi river basin and Musi river drainage, South Sumatra (Indonesia) [29]. F. signifer is matrotrophic viviparous, with the uterine embryos gaining nutrients from lipid- and proteinrich histotroph secreted from villus-like uterine appendages, called trophonemata [28, 32, 33]

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