The best explanation regarding the survival value of a fish or frog species that lays hundreds of eggs compared to a species that lays only a single egg is:
More eggs laid increases the likelihood that more offspring will survive predation or failed fertilization.
This reproductive strategy is known as "r-strategy" (characterized by high fecundity, where organisms produce a large number of offspring with relatively low parental investment in each), which increases the chances that some offspring will survive despite high rates of predation and other environmental challenges. In contrast, species that lay only a single egg tend to invest more care or resources into that single offspring, which is characteristic of "K-strategy" (where organisms produce fewer offspring but invest more effort into their survival).
Thus, the high egg count in certain species serves as a way to increase the overall likelihood of some young reaching maturity, despite high odds against any individual offspring's survival.