פירוש על עבודה זרה 79:6

A boat-load of fish called “tzahanta” comes in to town, but it is unclear whether these fish are kosher. There are no identifiable signs of kashrut on the fish themselves (probably because they are minced), but they can see scales on the sides of the boat. R. Huna b. Hinnena declares the fish to be kosher, assuming that the scales on the sides of the boat come from the fish in the boat. But Rava notes that many fish have scales. How do we know that the scales come from these fish and not from others? Each amora issues declarations prohibiting or permitting the fish. What a conflict!