Biology of Finfish and Shellfish (2+1)

4.4.1.2. Volumetric method

After separation in Gilson’s fluid, the cleaned eggs are put in a measuring cylinder and made up to a known volume with water. Subsamples are drawn by shaking the container until all the eggs are evenly distributed throughout the water. A subsample of known volume is again drawn with a pipette, and the number of eggs in the subsample is counted. Then the fecundity is calculated as follows.

F = nV/v (Where, n = number of eggs in the subsample, V = volume which contain all the total eggs and v = volume of the subsample).

In practice, it is normally necessary to count eggs from more than one subsample from each fish to get a reliable estimate of the fecundity.

This method is subject to considerable bias because it is very difficult to get all the eggs evenly distributed throughout the measuring cylinder. Unless great care is taken, the density of the eggs will be more at the bottom of the cylinder than in the top and middle of the cylinder.