ULTRASTRUCTURE AND PROTEIN-UPTAKE OF THE EMBRYONIC TROPHOTAENIAE OF 4SPECIES OF GOODEID FISHES (TELEOSTEI, ATHERINIFORMES)

Embryos of most species within the viviparous teleost family Goodeidae develop characteristic perianal processes that are considered to be d erivatives of the embryonic hindgut. These processes, termed trophotae niae, are covered with an epithelium that is continuous with the absor ptive epithelium lining the hindgut. Gestation is intraovarian, and tr ophotaeniae mediate the uptake of maternally provided nutrients into t he embryo from the ovarian fluid. Ultrastructural examination of the t rophotaeniae of four goodeid species reveals substantial diversity in the organization of the epithelium within the family. The trophotaenia e of Alloophorus robustus, Zoogoneticus quitzeoensis, and Ilyodon furc idens have morphological features associated with the endocytosis of m acromolecules and can be shown to endocytose the exogenous protein tra cer horseradish peroxidase (HRP) rapidly. The trophotaenial epithelia of these species differ from one another with respect to other morphol ogical features such as cell height, organization of the brush border, and the complexity of the intercellular spaces. The trophotaeniae of Goodea atripinnis lack an endocytotic apparatus and do not endocytose HRP. However, the overall organization of G. atripinnis trophotaenial cells suggests a function as a transporting epithelium. The cells have a dense brush border, numerous mitochondria, and many mitochondria th at are enveloped by lamellar sheets of intracellular membrane. Post-fi xation with osmium and potassium ferrocyanide reveals a marked differe nce in the complexity of the subepithelial connective tissue. Alloopho rus robustus and Z. quitzeoensis exhibit an extremely electron-dense g round substance containing many acellular components. Goodea atripinni s exhibits an electron-lucid ground substance with few acellular compo nents. (C) 1994 Wiley-Liss, Inc.