By W.S. Hoar and D.J. Randall (Eds.)
FROM THE PREFACE: Dramatic alterations ensue within the body structure of such a lot animals in the course of their improvement. one of the vertebrates, birds are solely oviparous, stay for variable classes in a cleidoic egg, and exhibit basic adjustments in excretion, foodstuff, and breathing on the time of hatching. against this, the eutherian mammals are all viviparous, rely on the maternal stream and a really good placenta to supply meals, alternate gases, and discharge wastes. The body structure of either mom and fetus is extremely really expert in the course of gestation and adjustments essentially on the time of delivery. Fishes exemplify either the oviparous and the viviparous modes of improvement, with a few examples which are intermediate among the 2. In those volumes, chosen reports of many, yet no longer all, features of improvement are awarded. The chapters partly A relate to the body structure of eggs and larvae; these partially B quandary viviparity and the body structure of posthatching juvenile fishes.
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Extra resources for The Physiology of Developing Fish: Viviparity and Posthatching Juveniles
During the past 25 years, a number of reviews have appeared on the subject of the reproductive endocrinology of fishes and related topics. They show that what is needed is information specifically dealing with endocrine influences on gestation, copulation, motheryoung relations, the development of placenta-like structures, superfetation, parturition, etc. Unfortunately, there are few pertinent original papers and reviews. Pickford and Atz (1957, pp. 216-222) reviewed the evidence for pituitary control over viviparity in fishes up to 1956.
Viviparity also may be advantageous in environments with changing local conditions. Live bearers’ broods are portable, and they are easily moved away from place where conditions are deteriorating (Baylis, 1981). Viviparity may facilitate dispersal or recolonization, inasmuch as a single pregnant female has the potential to colonize a new environment. Finally, viviparity offers the advantages of parental care with none of the constraints on mobility so often associated with the care of offspring.
Approximately 3% of all the teleost families have viviparous members, but 57% of those with internal fertilization are viviparous (Wourms, 1981; Gross and Sargent, 1985). Similarly, 65% of the chondrichthyan species, all of which display internal fertilization, are viviparous (cf. Section I,A,l). Attempts to identify ecological conditions that favor viviparity in 28 JOHN P. WOURMS ET AL. fishes have led to some general observations regarding the relationship between ecology and viviparity and the maternal-embryonic relationship.