Zaat(1971)

An obsessed scientist, Dr. Kurt Leopold - who has been scorned by his peers - is convinced he can transform humans into fish. In his isolated backwoods laboratory, he proves his hypothesis by turning himself into a horrible, vengeful creature that is part man, part walking catfish! Bent on revenge and determined to turn the tables on humanity by making his fishy friends the dominant species on Earth, all that stands in his way are a small town sheriff, a dedicated young biologist and a couple of swinging agents from the Inter-Nations Phenomenon Investigations Team (INPIT). It's a southern fried fight to the finish (Florida style!) with the ecological state of the entire planet at stake!