Analysis of early developments in a viviparous fish Xenotoca eiseni

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I analyzed a mechanism of non-mammalian viviparous system using a live-bearer teleost Xenotoca eiseni. The viviparous fish doesn't possess defined analog of fetal organs corresponding to a placenta and an umbilical cable of mammals. They have unique ribbon-like structure elongated from a perianal. This structure is presumed to be a functional analog of the fetal organ of mammals, which plays a role for absorption of maternal nutrients. I found that the ribbon-like structure of the fetal fry is disrupted by programed cell death in perinatal stage. Such regression mechanism has not reported in mammals. It was presumed to be a unique system in viviparous fish.