The reproductive biology and gonad cycle of three Cyprinid fish species : Barbus canis (Valenciennes, 1842), B. longiceps (Valenciennes, 1842) and Capoeta damascina (Valenciennes, 1842), in the upper Jordan River system of Israel were studied by monthly sampling over a two-year period . The reproductive activity of the three species was found to peak from January to April, mostly involving upstream migration towards spawning grounds on river beds 400-900 m above the Jordan River . Hybrids of the three species were collected in nature : in those of Barbus canis x Capoeta damascina, the gonads possessed both types of gametes, spermatogonia and oogonia, all of which became arrested at an early stage of development, and infertile ; in hybrids of B. canis x B . longiceps detected in nature, males had oocytes dispersed in the testis, whereas in females, the ovaries had small islets of spermatogonial tissue . In these female hybrids the oocytes ripened normally and spawning occurred . 79

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