Yolk utilization in Scyliorhinus canicula, an oviparous dogfish

Abstract

SynopsisUsing plastic embedding techniques and semithin sections, in order to overcome the difficult sectioning of yolky eggs, we have been able to carry out histological study of the external yolksac from fertilization until birth in the oviparous dogfish Scyliorhinus canicula. The endoderm and its contacting giant yolk nuclei remained very flat, seemingly inactive, during the larger part of development They became activated only when the external yolksac (EYS) began to shrink. This activation increased along a vegetal-animal gradient in the EYS, but it was essentially restricted to the parts located near the yolk stalk. A statistical study of oocyte, yolk, embryo and newborn fresh and dry weights confirmed that the mass of dry tissue in the embryo (30mg) and in EYS wall (<1mg) at mid-development were still very low compared to 0.B-l.5g mass of yolk available for development. This explains why yolk weight remained practically the same during the first half of development. The end of this first period was marked by entry into the pre-hatching state at 85-115 days under laboratory conditions (14-16 D C). At this time, yolk began to enter the spiral gut, where it was digested during the second half of development and during one week period after eclosion. Eclosion occurred 170-220 days after egg laying or extraction from oviduct. Two internal storage organs were studied biometrically in the newborn: the internal yolksac (IYS), and the liver, which was fully developed at birth. Both IYS and liver dry weights corresponded to about 10% of the original yolk, while the gut was only 2 %, and the rest of the newborn body 58%. Thus, about 20% of yolk dry mass was consumed during development, a figure that is low for oviparous animals.

Urea-based osmoregulation in the developing embryo of oviparous cartilaginous fish (Callorhinchus milii): contribution of the extraembryonic yolk sac during the early developmental period

“…Taken together, our findings indicate that urea is produced in the endodermal layer of the YSM, and is then excreted into nearby blood vessels, and subsequently transferred to the embryo in order to maintain a high concentration of urea in the body fluid. Yolk sacs are found in many vertebrates, and the extra-embryonic YSM has been considered to play a key role in the absorption of yolk nutrients (Lambson, 1970;Diez and Davenport, 1990;Lechenault et al, 1993;Zohn and Sarkar, 2010;Bauer et al, 2013). An intriguing finding on the role of the YSM in teleost fish is that it is involved in osmoregulation during early development .…”

Gestational morphogenesis of the uterine epithelium of the gummy shark (Mustelus antarcticus)

“…Oviparous species and lecithotrophic viviparous species continue to be yolk reliant throughout gestation. Other viviparous species display diverse methods of providing maternally derived nutrients either through uterine secretions (histotrophy), ova (ovatrophy), siblings (intrauterine cannibalism or adelphotrophy), or placental transfer (placentatrophy) (TeWinkel, 1943;Von Bonde, 1945;TeWinkel, 1963;Jollie and Jollie, 1967b;Baranes and Wendling, 1981;Wourms, 1983, 1984;Hamlett, 1987Hamlett, , 1989bHamlett, , 1993Hamlett et al, 1993c;Lechenault et al, 1993) Eight modes of reproduction have been described for viviparous chondrichthyans. Lecithotrophic viviparity is a reproductive mode in which no placenta is formed, the uterine mucosa develops vascularized flaps, folds, or villi and the embryos rely on yolk sequestered in the yolk sac that persists throughout gestation.…”

Dogmas and controversies in the handling of nitrogenous wastes:Osmoregulation during early embryonic development in the marine little skate Raja erinacea; response to changes in external salinity

“…Lechenault et al (1993) reported that the liver constituted only 4.8-6.8% of the total body wet mass of Scyliorhinus canicula (an oviparous dogfish) neonates. If one assumes that all of the CPSase III activity is localized in the liver of R. erinacea embryos, then we have severely underestimated the hepatic CPSase III activity in embryos.…”