ABSTRACT
Approximately 70 unisexual biotypes of fi shes, amphibians and reptiles are presently recognized (Vrijenhoek et al., 1989). Although the greatest number of unisexuals recorded are lizards, the rearing diffi culties limit the possibilities of experimental manipulations. Only seven unisexual biotypes of fi shes are described and all of them are readily amenable for rearing and experimentation (Table 16). In fact Hubbs and Hubbs (1932), the fi rst to discover the very existence of unisexual vertebrates, have reared and experimented with the Amazon molly Poecilia formosa for 15 years (Schultz, 1973). At the Museum of Zoology Department, University of Michigan, Poeciliopsis monacha latidens were reared over a period of 29 years during which the fi sh underwent 60 generations (Schultz, 1989). According to Wu et al. (2003), the unisexual complex of the crucian carp Carassius auratus was reared at the Institute of Hydrology, Wuhan for a minimum of 4 generations, covering a period of not less than 5 years. Not surprisingly, in relation to the small number of species, a relatively large volume of literature is available for unisexual fi shes.
