Question

Every spring, each mature female fish of a particular species produces several million eggs. however, the total population of this species remains at around 10000 from one year to the next. state two reasons why the fish population remains approximately the same from one generation to the next

Answer 1

One of the reasons why the fish population remains approximately the same from one generation to the next is because not all the eggs laid will survive to adulthood. There are several factors which bring about elimination of the the newly hatched eggs. Examples of these are predators and diseases which eliminate the young offsprings at different stages before they develop into adulthood. 
Secondly, production of many eggs by the different fish species leads to competition for survival. Resources such as water, food, oxygen and shelter have to be fought for and its only the fittests that will be able to survive till the reproduction stage.