fish lays thousands of eggs because some of them are eaten by big animals and some of them don't get enough Oxygen and some more things that they can't grow , So fish has to lay many Eggs so that so of them becomes a new one.

Who do fish lay many eggs?

Rather, the rate of predation on fish eggs is high because they produce such a lot of eggs. Many fish produce thousands of minute eggs, each with an infinitesimally small chance of survival because this reproductive strategy in these species results in the highest number surviving to adulthood.

Why do female fish need to produce so many eggs?

Fish and amphibians will typically produce more eggs while reproducing than mammals and reptiles. This is due, in part, to the method of egg fertilization during which amphibians and fish fertilize the eggs externally, while mammals and reptiles fertilize eggs internally.