Normal embryonic stages of Polyodon spathula (Walbaum)

The paddlefish, Polyodon spathula (Walbaum), is a degenerate survivor of the Cretaceous chondrostean family Polyodontidae. Except for its anatomy, the biology of this sharklike “living fossil” is almost unknown. Some aspects of its gametogenesis are I record (Larimore, ’ 5 0 ) , but only a dozen or two postlarval young have been collected (Thompson, ’33), and the observations published on its life history have been extremely scanty. This is unusual for such a conspicuous species, whose individuals may grow to a length of seven feet and a weight of 160 pounds. Polyodon has been fished commercially at a number of places along the Mississippi River system, but in each case the resource was soon exhausted. Local renewal of the population has been noticed in recent decades where new breeding grounds were established above certain great power and storage dams. At one of these, on the upper Osage River near Osceola, Mo., Polyodon was seen spawning for the first time in ’60, by Charles Purkett. That year he collected the first eggs and newly hatched larvae ever seen (Purkett, ’61), and the next year he stripped and fertilized eggs from mature fish caught near the same place by sportsmen. Some of the young fish which developed from these eggs reached a length of nearly three feet at the age of 17 months (Purkett, ’63a). The Fisheries Section of the Missouri State Conservation Commission is making life history and population studies on Polyodon, with a view to stabilizing and increasing its numbers as a permanent resource (Purkett, ’63b). Since it is not yet clear that Polyodon succeeds in spawning normally every year, the junior author of this paper is investigating the possibility