Chronology of spermatogenesis and spermiogenesis in poeciliid fishes

Analysis by autoradiography after a single pulse label with 3H‐thymidine was used to mark the chronology of cell progression through spermatogenesis and spermatid differentiation in the ovoviviparous teleost fish, Poecilia sphenops, the aquarists' “black molly.” A minimum of 21 days was required from initiation of meiotic prophase to the development of mature, aggregated sperm. An additional two weeks elapsed during transport of sperm through testicular ducts, so that shed spermatophores with labeled sperm were found only after 35 or more days following isotope injection. Time estimates for various stages of spermiogenesis were independently confirmed by assessment of the duration of elapsed time using frequency of occurrence of particular stages within the total population of testicular crypts as an index of relative elapsed time.