You thaw incorrectly
Thawing at room temperature or with hot water provides ample opportunity for bacteria to grow. Instead, thaw fish for four to five hours in the refrigerator. If you need to thaw quickly, seal it in a zip-top bag and place it in a bowl filled with very cold water. “The bag should be completely covered with water, but make sure the meat itself doesn’t come into contact with the water,” says Tentori. “If it does, it will become too moist and very hard to cook.” This method will thaw a filet of fish in about 20 to 30 minutes.