Leviticus 11:10

All that have not fins nor scales— These, according to Dr. James, are what medicinal writers call pisces molles, the soft kind of fish: and, as all kinds of fish are very subject to alkaline putrefaction, so those without scales incline sooner and more to putrefaction, than those furnished with scales; and shell-fish most of all. The Egyptian priests abstained from fish of all sorts; as did also some of the worshippers of the Syrian goddess: and Calmet observes, that among the ancient Romans it was not lawful to use fish without scales in the feasts of the gods.

Note; Though Christians enjoy perfect liberty in the moderate choice of all the good creatures of God, yet God's Israel will still deny themselves many things in which others indulge themselves.