Question

why do you think it is necessary for frogs and fishes to lay so many eggs at a time

Answer 1

Yes, because they lay eggs out side their body and hence it becomes risk of predators.

Answer 2

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Though fish and frogs lay hundreds of eggs all the eggs do not get fertilized and develop into new individuals.

This is because the eggs get exposed to water movement, wind and rainfall. Also, there are other animals in the pond which may feed on eggs.

Thus, production of large number of eggs is necessary to ensure fertilization of at least a few of them.

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