Normal ejaculate when a man is not drained from prior sex and is suitably aroused, is around 2 - 6 ml, although this varies greatly with mood, physical condition and sexual activity. Of this, around 1% by volume only is sperm cells. Hypospermia, a semen volume of under 1.5 ml, would only usually be a factor in infertility if the two conditions are combined.
The presence of high levels of fructose (a sugar) is normal in the semen and this comes almost entirely from the seminal vesicles. Obstruction of this accessory gland will result in low semen volumes since the seminal vesicles normally produce 70% of the seminal plasma. A test that showed low fructose levels combined with a low semen volume would therefore suggest an obstruction in this part of the body.