WOURMS, J.P.*; KRUEGER, D.; Clemson University; Clemson University: Gycogen in Gut-Based Embryonic Nutrition of Ataeniobius toweri, A Viviparous Goodeid Fish with Rudimentary Trophotaeniae.

A. toweri, long considered the only goodeid whose embryos lack trophotaeniae (external hindgut derivatives), actually have rudimentary trophotaeniae equivalent to an early stage in other goodeids, e.g. Ameca. Prior to parturition, trophotaeniae regress and the vent from the posterior gut is reorganized into a proctodeum. A. toweri embryos are matrotrophic and increase 29X in dry weight during gestation. Nutrient uptake is primarily gut-based. Although small ridges and villi amplify its surface area, the gut is not hypertrophied. Unlike other goodeids, glycogen appears to have a significant role in the nutrition of A. toweri embryos. Lipids and proteins also may be involved. TEM reveals extensive deposits of glycogen rosettes and some lipid inclusions in maternal ovarian epithelial cells. Small glycogen (?) particles occur in the ovarian fluid which is imbibed. Nutrients are taken up by gut cells. The foregut may be involved with lipids. Glycogen uptake via endocytosis seems to occur both in hindgut and trophotaenial cells. They are identical in structure. These cells have prominent microvilli, many apical canaliculi or caveolae, and coated pits and vesicles. There is a well developed apical system of early tubular endosomes (?) and small spherical vesicles. Many large vesicles that contain glycogen-like particles occur in the apical and perinuclear cytoplasm. Large circular aggregates of SER also occur. Nuclei are basally located. Glycogen-like particles occur in the basal lamina and associated capillaries. Embryonic liver cells are almost completely filled with glycogen, except for several large lipid or lipoprotein inclusions, the nucleus, and occasional mitochondria and patches of ER. (Supported by NSF).