Why do fish and frog produce a huge number of eggs each year?

The type of fertilization in fish and frog is external fertilization i.e fertilization takes place outside the body. In fish and frog fertilization takes place in water. As the chance of fertilization is nature dependant i.e it depends on the movement of water for the sperm to come in contact with the egg. Thus the fish and frog produce a huge number of eggs each year to overcome the chance factor(sperm to come in contact with egg) and produce offsprings.