The Mating of Fish The female fish lays her eggs in shallow water. The male, swimming several feet or yards behind the female expells from his body the many sperm cells which are to be used in fertilizing the eggs. It will be observed that there is no sexual contact between the male and female fish at the time the eggs are fertilized. Several days before this event, these fish might have been seen on the riffles, or in deep water, swimming along side of against and over each other. Many mistake the action of the fish at this period for mating. They are not mating, they are love-making. Sexual 'excitement is necessary to the development of the eggs in the ovaries of the female, and especially for the generation of thousands of sperm cells by the male. From this we see that the function of these demonstrations among fish is sexual excitement.