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Document Type

Book Chapter

Department/Program

Virginia Institute of Marine Science

Editors

John A. Musick, Virginia Institute of Marine Science
Ramon Bonfil, Wildlife Conservation Society

Publication Date

2005

Book Title

Management Techniques for Elasmobranch Fisheries

Publisher

FAO

City

Rome, Italy

Series

FAO Fisheries Technical Paper 474

Abstract

Several reproductive specializations are found within the elasmobranchs. All elasmobranchs fertilize internally and produce a relatively small number of large eggs. Elasmobranch fecundity generally ranges from one to two offspring produced a year up to a maximum of 300 in the whale shark (Compagno, 1990; Joung et al., 1996). Elasmobranch reproductive strategies include oviparity, aplacental viviparity and placental viviparity (Wourms, 1977). Oviparous species enclose eggs in an egg case and deposit them into the environment, where embryos develop external to the body of the mother . .Embryos remain in the egg case to develop for a period ranging from less than two months to over one year (Compagno, 1990). Viviparous species retain eggs within the uteri where the embryos develop. The yolk sac of placental viviparous species interdigitates with the uterine wall to form a placenta in which nutrients from the mother are transferred to the embryo. In most species the egg envelope is retained and incorporated into the uteroplacental complex (Hamlett, Wourms and Hudson, 1985). Gestation for viviparous species ranges from less than six months to greater than two years (Compagno, 1990). Viviparous species may have either lecithotrophic or matrotrophic development. Lecithotrophic development occurs when embryos derive their nutrition solely from yolk reserves and occurs in many aplacental viviparous species. Matrotrophic development occurs when embryos supplement the yolk reserves by obtaining maternally derived nutrients during gestation and also occurs in many aplacental species and all placental viviparous species (Wourms and Lombardi, 1992). The advantage of matrotrophy may be the increase in juvenile size at birth and therefore increased survivorship of young. Another important consideration in the evolution of elasmobranch reproductive strategies is the presence or absence of uterine compartments. Uterine compartments are formed in all species with placental development and some species with aplacental development and are believed to be an important step in the evolution of placental viviparity (Otake, 1990).

ISBN

92-5-105403-7

Reproductive biology


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