I don't know why I never sought out Lovecraft's essay "Supernatural Horror in Literature" before now, but it does contain a reference to Irvin Cobb's story "Fishhead":
"Still further carrying on our spectral tradition is the gifted and versatile humourist Irvin S. Cobb, whose work both early and recent contains some finely weird specimens. 'Fishhead', an early achievement, is banefully effective in its portrayal of unnatural affinities between a hybrid idiot and the strange fish of an isolated lake..."
[Lovecraft was, unfortunately, an avowed racist and his language here cannot be excused.]

You could always sell the book back thru Amazon.com if you found you didn't like it or donate it to a library. Or you could check out your local library, read the stories, or have them buy the book/stories so you can read them.