When a farmer plants a field he doesn't hope that 25% of his seeds grow. He hopes every one of his planted seeds produces a plant. The same holds true for fish hatcheries.

The better our fertility the more efficiently these facilities operate. Average egg survivals in the Iowa hatchery system has historically been between 60 and 70%. The multiple addition of semen during walleye egg fertilization has been the most recent spawning technique evaluated. This technique has given egg survivals of 83.0 to 89.0% while the conventional, single semen addition technique gave egg survivals ranging from 68.0 to 74.0%. In addition, the depth of the eggs in the egg pan (to which the semen is added) at the time of fertilization is an important factor. Depths of 4.0 mm have given significantly higher egg survivals that depths greater than 7.0 mm. Why does this work? It's probably related to the surface area to volume ratio. Simply, more eggs come into contact with the semen at shallower egg depths.