What episode in star trek has creatures that leave sucker marks on Spock and they also fly are flat like a flounder.?

The episode you're looking for is "The Man Trap", the very first episode of Star Trek: The Original Series.

The creatures in this episode are called Salt Vampires, and they are flat, fish-like creatures that resemble flounders. They feed on salt, and they leave behind sucker marks on their victims, which are very prominent on Spock.