No, I haven't experienced any problems with this. But it was just a thought that occured to me. It seemed possible that some sort of disease from fresh supermarket bought seafood could end up in my tank. I make my own fish food with ground up squid, shrimp, and clams. I'm not sure if the freezing process would kill anything potentially harmful. I was also wondering if the commercially available fish foods made by Ocean Nutrition, etc. somehow treated their food to avoid any of these problems.
For since the creation of the world God's invisible qualities...have been clearly seen, being understood from what has been made, so that men are without excuse. (Romans 1:20)