These shall ye eat of all that are in the waters: whatsoever hath fins and scales in the waters, in the seas, and in the rivers, them shall ye eat.

Wesley's Notes

11:9 Fins and scales - Both of them; such fishes being more cleanly, and more wholesome food than others. The names of them are not particularly mentioned, partly because most of them wanted names, the fish not being brought to Adam and named by him as other creatures were; and partly because the land of Canaan had not many rivers, nor great store of fish.

Jamieson-Fausset-Brown Bible Commentary

9. These shall ye eat . whatsoever hath fins and scales-"The fins and scales are the means by which the excrescences of fish are carried off, the same as in animals by perspiration. I have never known an instance of disease produced by eating such fish; but those that have no fins and scales cause, in hot climates, the most malignant disorders when eaten; in many cases they prove a mortal poison" [Whitlaw].

Matthew Henry's Concise Commentary

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.
]