Looking at this from a very different angle,there might be more to this rumor than meets the eye.
Some herbicides have spectacular results on fish. Specially a herbicide that is used when growing cucumbers. The cukes are perfectly fine for human consumption after application. However,when this herbicide is spread in the water,it causes a big fish kill. Again,the killed fish is perfectly fine for human consumption. Illegal "fishing" with this chemical is a real problem in Israel in the sea of Galilee. The killed fish makes its way to the fish market in Tiberias. Maybe somebody around here picked up on this trick.