Analysis of the post-vitellogenic oocytes of three species of Danubian Acipenseridae

Post-vitellogenic oocytes of beluga (Huso huso Linnaeus, 1758), Russian sturgeon (Acipenser gueldenstaedtii Brandt, 1883) and sterlet (Acipenser ruthenus Linnaeus, 1758), sampled downstream of the ``Iron Gate II'' dam on the Danube River, were characterised according to diameter, dry mass, water and protein contents. All oocytes examined were ovoid in shape with the major diameter being measured in the animal-vegetal axis. The beluga oocytes were the largest, with major and minor diameters of 4.18 +/- 0.13 and 3.61 +/- 0.14 mm, respectively. The oocytes of the Russian sturgeon were the next largest, with major and minor diameters of 3.69 +/- 0.16 and 3.36 +/- 0.15 mm, respectively, while those of the sterlet were the smallest, with major and minor diameters of 2.40 +/- 0.10 and 2.14 +/- 0.07 mm, respectively. Values for oocyte wet and dry mass (mg/ind) ranged from 25.9-32.1 for wet mass and 12.2-15.5 for dry mass of the beluga oocytes, 18.9 +/- 1.4, and 9.01 +/- 0.12 for wet and dry mass of the Russian sturgeon oocytes, to 6.5 +/- 0.3 and 3.07 +/- 0.14 of the sterlet oocytes. The water content of the oocytes of all three sturgeons was very similar (51-53 \% of wet mass). The protein content (\% of dry mass) was highly conservative among the species at 53.0 +/- 2.0, 55.9 +/- 3.8 and 50.0 +/- 1.2 for the oocytes of beluga, Russian sturgeon and sterlet, respectively.