Lipoprotein Biology During Induced Oogenesis in the Shortfinned Eel, Anguilla australis—Vascular Transport

The ecological, cultural and economic importance of freshwater eels, coupled with declining wild populations, drives the need for artificial propagation of these fish. Despite the closure of the lifecycle in captivity over a decade ago, numerous bottlenecks still prevent production at a commercially viable scale. Focusing on the key event of nutrient accumulation, we employed hypophysation over a 10-week period with biweekly sampling of female New Zealand shortfinned eels (Anguilla australis). Slotblots, colorimetric lipid/cholesterol assays, fast protein liquid chromatography and radioimmunoassay were used to assess aspects of blood chemistry. The lack of any trend in triglyceride and apolipoprotein B levels in plasma over time, combined with a significant reduction in cholesterol concentrations and a 10-fold increase in vitellogenin levels, confirmed a shift from low-density lipoprotein dominance—usually associated with lipid uptake and early oogenesis—to an abundance of high-density lipoproteins linked to vitellogenesis. The ongoing presence of 11-ketotestosterone in the circulation and the increase in 17β-estradiol levels reinforced the importance of steroids in mediating the gonadotropic signal associated with hypophysation. We conclude that the accumulation of both vitellogenin and apolipoprotein-B-associated lipids is essential for nutrient accumulation in eel oocytes during artificial induction of maturation.