Teenage Mutant Ninja Turtles (1987): Season 4, Episode 25

4 - 25: Rebel Without a Fin

Dr. Polidorius, a mad scientist plotting to mutate all humanity into aquatic-beings, creates Ray (not the similarly-named Mighty Mutanimals character), who possesses several abilities of different marine species. Ray kidnaps April O'Neil, and Polidorius mutates her into a fish-woman to be Ray's mate.