I think the industrial ice guys filter the water during the process and remove most chlorine anyway. Dechlorniator is cheap and easy to be on the safe side. I wouldn't change the water temp more than 8-10 degrees from where you caught them but keep in mind the surface temp is generally not the temp where you got em when dealing with herring (alewife, which are commonly incorrectly called shad). Now gizzards are another story.