Cool water is better.

If the water is boiled and then put the fish and bones, the protein on the surface of the raw material is rapidly coagulated and denatured, the cell pores are closed dramatically, while the raw material has not reached the internal denaturation temperature, the internal and external denaturation speed is too big a difference, when the internal denaturation temperature is reached, the surface of the surface has been coagulated and denatured, the pores are closed to the proteins and other substances will hinder the internal flavor of the material Dissolution, the freshness of the soup is significantly reduced.