Comparative Microanatomy of the Gravid Oviduct in Egg-laying and Live-bearing Sharks

Student: 
Shraveena Venkatesh

Sharks show varying reproductive strategies but the female reproductive tracts of all these species show the same basic structure with oviducts modified to form oviducal glands, isthmuses and uteri. Oviducts from eight specimens of different maturities of the aplacental viviparous species, Squalus acanthias and three gravid specimens of the oviparous species, Scyliorhinus canicula were sectioned, processed, stained and compared. The anterior oviducts of the two species show a similar structure. The isthmus of S. acanthias was also described. Sections of the uterus, of this species at different stages of maturity show changes in surface area, extent of vascular supply and the presence of large granular secretory cells. The uterus of S. canicula differs from the former in complexity of epithelial folding, degree of vascularization and secretory products. Gravid uteri of both species are structurally specialized for their respective purposes, to accommodate embryos and facilitate the processes that contribute to their growth and development.