מדרש על ויקרא 11:12

11) (Vayikra 11:12) "Whatever has no fins and scales in the water is detestable to you." What is the intent of this? (i.e., it has been stated already.) I might think (that it is permitted) only when it brings its signs of cleanliness with it to the dry land. If it left them in the water, how do I know (that it is still permitted)? From "in the water." "it is detestable to you": it is forbidden to trade in them.