it exactly what the title tell you . an island inhabit by fishmen . shipwreck doctor claudio cassinelli and crew land on the island and theyre either pick off by the fishmen or rope into work for treasure hunt lunatic richard johnson . cassinelli discovers that johnson and who believe he find the lost city of atlantis and have be keep disgraced scientist joseph cotten and his daughter barbara bach hostage for 15 year so the fishmen can uncover a treasure trove beneath the sea . cotten and of course and be a complete madman . bach and cassinelli have great chemistry . this insanity be direct by sergio martino and be not and surprisingly and without merit . it fast pace and reasonably well act and the fishmen look pretty convincing ( though it unlikely anyone could prove that these thing dont look like actual fishmen ) . there an excellent music score by luciano michelini .