Sundayan fish

Sundayan fish were numerous but not well-catalogued by humans by the time the Doctor and Martha visited the planet Sunday in 2108. Resident Candy Kane noted that the fish on Sunday had become scarce following the cataclysmic flood that befell the First Wave of colonists in late 2107 or early 2108. Kane knew of at least one specific kind of fish, although it is unclear if she ever knew its name. According to her, this unnamed fish species was small with extremely sharp teeth. Once they had burrowed through the skin of a human, they would remain there, even if the fish's head was separated from the rest of its body. (NSA: Wetworld)