(10) Of all that move in the waters.--That is, apart from the fishes exhibiting the above-named signs, all other inhabitants of the water are forbidden. Hence all shell-fish, whether molluscs or crustaceans, and cetaceous animals, are unclean.

11:1-47 What animals were clean and unclean. - These laws seem to have been intended, 1. As a test of the people's obedience, as Adam was forbidden to eat of the tree of knowledge; and to teach them self-denial, and the government of their appetites. 2. To keep the Israelites distinct from other nations. Many also of these forbidden animals were objects of superstition and idolatry to the heathen. 3. The people were taught to make distinctions between the holy and unholy in their companions and intimate connexions. 4. The law forbad, not only the eating of the unclean beasts, but the touching of them. Those who would be kept from any sin, must be careful to avoid all temptations to it, or coming near it. The exceptions are very minute, and all were designed to call forth constant care and exactness in their obedience; and to teach us to obey. Whilst we enjoy our Christian liberty, and are free from such burdensome observances, we must be careful not to abuse our liberty. For the Lord hath redeemed and called his people, that they may be holy, even as he is holy. We must come out, and be separate from the world; we must leave the company of the ungodly, and all needless connexions with those who are dead in sin; we must be zealous of good works devoted followers of God, and companions of his people.
]And all that have not fins nor scales in the seas, and in the rivers,.... Such as eels, lampreys, &c.

of all that move in the waters, and of any living thing which is in the waters; the former of these are interpreted by Aben Ezra and Ben Gersom of little fishes that have but a small body, and such as are created out of the waters; and the latter, of such as are produced of a male and female; or, as Maimonides (r) explains it, the one signifies the lesser creatures, such as worms and horse leeches; the other greater ones, sea beasts, as sea dogs, &c.

they shall be an abomination to you; not only unclean, and so unfit to eat, but to be had in abhorrence and detestation, as being exceeding disagreeable and unwholesome; and, as a learned man observes (s), to these prohibited in general belong all those animals in lakes, rivers, or seas, which are of a slow motion, and which, because of the slow motion of their bodies, do not so well digest their food; and for that may be compared with four footed beasts that have but one belly, and so unwholesome as they.

(r) Hilchot Maacolot Asuret, l. 1. c. 2. sect. 12. (s) Scheuchzer. ut supra, (Physic. Sacr. vol. 2.) p. 287.