Thomas F. Sørensen

Variations in antifreeze activity and serum inorganic ions in the eelpout Zoarces viviparus: antifreeze activity in the embryonic state.

The eelpout Zoarces viviparus is a common inhabitant in the shallow waters along the Danish coastline. Specimens were caught in the brackish (12-16 per thousand) Roskilde fjord where water temperatures range from >20 degrees C during summer to subzero in winter. The serum melting points found in Z. viviparus varied between -0.76 (September) to -0.94 degrees C (January). Eighty to 97% of the serum melting points could be attributed to sodium, chloride and potassium. Hysteresis freezing points showed seasonal variation varying from -0.83 (September) to -2.08 degrees C (February). Serum antifreeze activity showed a seasonal variation with high levels (>1.2 degrees C) in winter and low levels (<0.1 degrees C) during summer and autumn. Antifreeze proteins are responsible for this antifreeze activity. Antifreeze activity was also found in Z. viviparus during their embryological development in the female ovary. Embryo thermal hysteresis reached the maximum level (approx. 0.6 degrees C) during December and maintained this level until parturition in January. Antifreeze activity seems unaffected by diminishing ice crystal fractions at ice fractions below 0.1 whereas ice fractions above 0.1 caused a decline in antifreeze activity.

Vascular Arrangement and Ultrastructure of the European Eelpout Zoarces viviparus Ovary: Implications for Maternal–Embryonic Exchange

The structural basis for exchange between maternal serum and ovarian fluid in the viviparous teleost Zoarces viviparus was investigated. Casts of the ovarian vasculature showed that blood supply to the ovary is initially directed to the follicular appendages lining the ovarian wall through thick‐walled muscular arteries running along the ovary wall and within the follicular appendages. The follicles had a rich capillary network with diffusion distances between maternal blood and ovarian fluid comparable to those found for gill epithelia, suggesting this is the primary site of gas exchange between maternal plasma and ovarian fluid. Follicular capillary beds were continuous with those in the ovary wall and were eventually drained by the ovarian and intestinal venous systems. The barrier between ovarian fluid and maternal blood consisted of the endothelial cells of the maternal blood vessels and a layer of epithelial cells lining the ovarian lumen, with an intermittent layer of loose connective fibers. Junctional complexes between cells were predominantly anchoring junctions with the occurrence of occasional occluding junctions, supporting the possibility of paracellular transport from maternal serum to ovarian fluid of small molecular weight compounds. Heavy investment in keratin filaments suggests that follicles are tissues of high structural integrity. Evidence for protein synthesis in the ovarian lining was found in the form of Golgi apparatus and rough endoplasmic reticulum. Although numerous cytoplasmic vacuoles and secretory granules were present in both epithelial and endothelial cells, the fate of synthesized protein remains to be determined. Anat Rec, 2007.