Loach is any of about 175 species of small, slender, freshwater fish. Loaches live in mountain streams, lakes, and swamps in Europe, Asia, and Africa. Many loaches are flat on the underside, which allows them to lie on the bottom of fast-moving streams. Others have a rounder, more wormlike body. The mouth is on the underside of the head and is surrounded by 3 to 6 pairs of fleshy whiskers called barbels.