What you want to ask is what do you mean by treating fish with cotton pills? Kill fish with cotton medicine. According to the query of China Chemical Enterprise Alliance Network, this cotton medicine is called Sedan, which can seal the air in the water and let all the fish breathe out of the water. Some big fish will die if they don't come out Saidan (also known as endosulfan) pesticide is a kind of pesticide mainly based on cotton, which belongs to poisoning and gradually decomposes when wet. This product is highly toxic to fish. A bottle of Saidan pesticide can cure the fish in an 89-acre fish pond.