How can spraying insecticides decrease the number of fishes

when you spray insecticides, the spray will go into the dirt and kill the insects or it will runoff by rain into rivers and streams and end up into lakes. The fish will then eat it and die. Also, the fish might eat plants covered in the insecticides and die like that too.

Explanation:

Pesticides can reduce the availability of plants and insects that serve as habitat and food for fish and other aquatic animals. ... Spraying herbicides to kill all aquatic plants can result in severely low oxygen levels and the suffocation of fish.

the millers tale is the answer.