Flatfish rhymes with:
catfish, catfish, whitefish, angelfish, bottomfish, catfish, crawfish, cuttlefish, dealfish, dogfish, goldfish, goosefish, guardfish, icefish, jellyfish, jewfish, lungfish, needlefish, pipefish, queenfish, redfish, sailfish, shellfish, starfish, sunfish, swordfish, whitefish
Flatfish sounds like:
feldpausch, flatbush, flatfishes