Aspects of embryo nutrition and excretion among viviparous embiotocid teleosts: Potential endocrine involvements

Abstract

1. 1. Embryos of the viviparous embiotocid fishes develop free within the ovarian cavity from small eggs for approximately 6 months. The biochemical composition of ovarian fluid was determined and compared to serum constituents in three embiotocid species during the gestation phase. 2. 2. SDS-gel electrophoresis data showed that ovarian fluid collected from female Cymatogaster aggregata during late gestation was essentially devoid of serum peptides, but contained peptides absent from maternal serum. The ovarian fluid peptides are probably derived from the ovarian epithelial lining. 3. 3. Pregnant female ovarian fluid contained large quantities of urea, whereas the maternal serum was devoid of this metabolite. This suggests that embiotocid embryos, but not adults, produce urea as a nitrogenous waste: furthermore, ovarian membranes must be relatively impermeable to urea. 4. 4. Amino acids in the ovarian fluid of Cymatogaster basically correspond to those in maternal serum. but were, in most cases, at lower levels. Although absent from serum, phosphoethanolamine was present at high levels in the ovarian fluid of pregnant Cymatogaster, but not Hyslerocarpus Irciski, during late gestation. 5. 5. The principal amino compound, exclusive of urea, in the ovarian fluid of Hysterocarpus and Micrometrus minimus was taurine. Serum levels of glutamine, ethanolamine and taurine were elevated in pregnant embiotocids. 6. 6. Lipid levels were also elevated in maternal serum during late pregnancy. Precluding phospholipids, the concentration of lipids in ovarian fluids was considerably lower than in maternal serum. 7. 7. In Cymatngtisler and Hysterocarpus serum progesterone and estradiol levels were comparatively low during gestation, posing some doubt as to the significance of these steroids in maintenance of pregnancy. 8. 8. The possibility that embiotocids produce an estrogen-dependent, vitellogenin-like protein was examined. Studies with Cymatogaster and Hysterocarpus indicated that the embiotocids may be the only teleostean family yet known which do not produce a vitellogenin-like protein.