I’ve been looking everywhere for this weird children;s picture book where a boy gets turned into a fish. Perhaps by a magic fish? It’s not the “Rainbow fish” which is something that comes up when I google it. Though this fish may have been rainbow-ey. It was kind of melancholy, and beautiful and unsettling, with very colorful rich illustrations. The boy ends up in the water still with his human face but with the body of a fish, and maybe he had to found someone to help turn him back into a boy or something?
Lost Classics of Teen Lit: Name That Book! 