Adam Clarke on 1 Samuel 5:4

Only the stump of Dagon was left - Literally, Only דגן dagon (i.e., the little fish) was left. It has already been remarked that Dagon had the head, arms and hands of a man or woman, and that the rest of the idol was in the form of a fish, to which Horace is supposed to make allusion in the following words: -

Desinat in piscem mulisr formosa superne "The upper part resembling a beautiful woman; the lower, a fish."

All that was human in his form was broken off from what resembled a fish. Here was a proof that the affair was not accidental; and these proofs of God's power and authority prepared the way for his judgments.