Biology of Finfish and Shellfish (2+1)

4.4.1. Fecundity

The problem of estimating fecundity depends upon several factors such as: the absolute numbers of eggs produced the total or partial spawning nature of the fish and the immature eggs present which will be carried over to the next spawning season. The methods used in fecundity studies fall into three sections: (1) Random sampling of fish, (2) estimating the number of eggs and (3) analyzing the results in relation to other parameters. The fixatives and preservatives used are:

1. Formalin and
2. Modified Gilson’s Fluid

It was recommended that Simpson’s modification of Gilson’s fluid should be used in the fecundity estimation

60% alcohol - 100 ml

water - 880 ml

80% nitric acid - 15 ml

glacial acetic acid - 18 ml

mercuric chloride - 20 g

This mixture hardens the eggs and also liberates them from the ovarian tissues. The ovaries should be shaken periodically in the Gilson’s fluid to help loosen the ovarian tissues and to ensure rapid penetration of the preservative. After 40 hours of preservation, the eggs can completely be liberated from the tissue by vigorous shaking.