Embryonic growth and maternal nutrient sources in goodeid fishes (Teleostei: Cyprinodontiformes)

Abstract

AbstractMost species of the viviparous teleost family Goodeidae exhibit an unusual placental relationship. Embryos lay free within the single, hollow ovary where they are bathed by the ovarian fluid. Nutrients are absorbed from the fluid through distinctive perianal processes called trophotaeniae. Trophotaeniae represent the embryonic component of the placenta and may be functionally divided into protein endocytosing and nonendocytosing types. The maternal component of the placenta is the internal ovarian epithelium (IOE). Since embryos undergo dry weight increases ranging from 68‐ to 387‐fold compared to the dry weight of mature ova, there must be substantial nutrient transfer from the maternal organism during gestation. Transmission electron microscopy of the IOE of gravid females of three goodeid species fails to reveal evidence of significant synthetic activity by the IOE, although occasional budding of parts of IOE cells occur, and the IOE of one species, G. atripinnis, contains substantial amounts of lipid. Electrophoretic comparison of nongravid females of two species establishes that the protein pattern of the ovarian fluid is similar to that of the female blood serum. In gravid females whose embryos bear protein‐endocytosing trophotaeniae, protein is undetectable in the ovarian fluid during mid‐ and late gestation, suggesting efficient protein absorption by the trophotaeniae. In gravid females whose embryos bear nonendocytosing trophotaeniae, serum proteins are present in the ovarian fluid at midgestation, but are reduced to only a trace at late gestation suggesting possible imbibition by the embryos. © 1995 Wiley‐Liss, Inc.