Osmotic eel

Osmotic eels were an aquatic animal with medicinal uses.

In the 2150s, Doctor Phlox kept a female osmotic eel aboard the Enterprise. (Star Trek: Enterprise)

In 2151, Phlox used his eels to heal Captain Jonathan Archer's leg wound. 

In 2153, Ensign Hoshi Sato was responsible for feeding Phlox's eel. 

In 2154, the eel was used to remove Xindi parasites from Sato. 

In 2155, Phlox used his eel to treat the wounded from the Tarod IX outpost after the Romulans attacked it.