Observations on the development of the male reproductive system in Gyrodactylus gasterostei Gläser, 1974 (Monogenea, Gyrodactylidae)

Abstract

SUMMARYThe development of the male reproductive system in Gyrodactylus gasterostei has been followed using parasites of known age maintained on isolated hosts. The penis develops shortly after the parasite has given birth for the first time (at an age of 24–30 h at 13°C) and the first active spermatozoa appear after 40–50 h. Spermatogenesis occurs more rapidly in G. gasterostei than in any other parasitic flatworm (including those from warm-blooded hosts) in which it has been measured, and the onset of male maturity is further hastened by a reduction in the number of pre-spermatogenic germ cell divisions. Spermatogonia have a diploid chromosome complement of 12, and spermatocytes undergo meiosis to produce haploid spermatozoa. No evidence of aneuploidy in spermatozoa was obtained. Although the development of haploid spermatozoa suggests that sexual reproduction can occur, production of embryos by isolated flukes which lack a mature male system indicates that other means of reproduction may also be employed.