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aqua 15(4)_ Cycles

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SINGLE PAPER

Volume 15, Issue 4 – 15 October 2009

José I. Castro: Observations on the reproductive cycles of some viviparous North American sharks, pp. 205-222

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SINGLE PAPER

Volume 15, Issue 4 – 15 October 2009

José I. Castro: Observations on the reproductive cycles of some viviparous North American sharks, pp. 205-222

Abstract
The reproductive cycle of sharks is defined by how often a species breeds and consists of two periods: vitellogenesis and gestation. These two periods can run concurrently or consecutively, and the duration of each period is variable. Together, the periods of vitellogenesis and gestation determine the length of the reproductive cycle. The genera Rhizoprionodon, Mustelus, and some Sphyrna exhibit annual cycles with concurrent vitellogenesis and gestation, and thus, they produce one brood each year. Carcharias taurus females apparently have a biennial reproductive cycle with discontinuous ovulation. Alopias spp. exhibit an annual cycle with concurrent vitellogenesis and gestation, and have continuous ovulation. Squalus acanthias has a squaloid biennial cycle with concurrent vitellogenesis and gestation. Sharks of the genera Carcharhinus, some Sphyrna, and Ginglymostoma have a biennial cycle with consecutive vitellogenesis and gestation. Galeocerdo cuvier has a 12-month gestation period in the western Atlantic, its reproductive cycle may be biennial. Carcharhinus obscurus has an 18-month gestation period and probably a three-year reproductive cycle. The biennial cycle, with all its variations, is found in sharks of different phyletic origins such as carcharhinoid, squaloid, and orectoloboid sharks, reflecting their common physiological processes that require a long time to accumulate sufficient energy to produce a brood.

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