Everything in the waters that does not have fins and scales is detestable to you.
Here is, 1. A general rule concerning fishes, which were clean and which not. All that had fins and scales they might eat, and only those odd sorts of water-animals that have not were forbidden, Lev 11:9, Lev 11:10. The ancients accounted fish the most delicate food (so far were they from allowing it on fasting-days, or making it an instance of mortification to eat...
Commenting on Leviticus 11:9-19
Whatsoever hath no fins nor scales in the waters,.... Which is repeated that they might take particular notice of this law, and be careful to observe it, this being the only sign given: that shall be an abomination unto you; the Targum of Jonathan says, that not only the flesh of such fish, but the broth, and pickles made of them, were to be an...
Whatsoever hath no fins nor scales, &c.--Under this classification frogs, eels, shellfish of all descriptions, were included as unclean; "many of the latter (shellfish) enjoy a reputation they do not deserve, and have, when plentifully partaken of, produced effects which have led to a suspicion of their containing something of a poisonous nature."