THE REPRODUCTION AND DEVELOPMENT OF SHARKS, SKATES, RAYS AND RATFISHES - INTRODUCTION, HISTORY, OVERVIEW, AND FUTURE-PROSPECTS

This volume had its origin in a Symposium on the Reproduction and Deve lopment of Cartilaginous Fishes that was held at the annual meetings o f the American Elasmobranch Society and the American Society of Ichthy ologists and Herpetologists in Charleston, South Carolina in June 1990 . The aim of this symposium was to bring together many of those scient ists interested in chondrichthyan reproduction and development in orde r to assess the current state of knowledge in these fields. The chondr ichthyan fishes occupy a pivotal position in comparative and evolution ary studies of vertebrate reproduction and development. They arc the o ldest surviving group of jawed vertebrates and they possess both the a dult vertebrate Bauplan and the vertebrate program of embryonic develo pment. The major features of the female reproductive system, including its embryonic origin, structure, physiological function, and biochemi stry, apparently were established early in vertebrate evolution and ar e fully developed in chondrichthyan fishes. These features of the fema le reproductive system have been retained during the evolution of the other classes of vertebrates. Much the same can be said for the male r eproductive system. Moreover. viviparity, placental nourishment of dev eloping embryos, and the hormonal regulation of these events made an i nitial appearance in this group. The twenty-two articles contained in this volume bring together a wide variety of complementary research by investigators from seven countries. It is hoped that presentation of this disparate body of research and thought in one place will provide perspective on current research activity, call attention to those area s in which the research endeavour is deficient, and identify opportuni ties for future study. The appearance at this time of a volume on the reproduction and development of cartilaginous fishes is quite opportun e. The continued existence of these fishes, which survived the great e xtinction events of Earth's history, is now threatened by over-exploit ation unless immediate steps for their conservation are undertaken. Kn owledge of their reproduction and development not only is an end in it self, but is of critical importance in devising successful conservatio n and resource management strategies.