Eel-like creatures used by Dr Phlox to clean and seal injuries, first seen treating Archer's leg wound in the Enterprise pilot Broken Bow.
The osmotic eel is one of the living remedies favoured by Dr Phlox, the Denobulan physician of Enterprise NX-01. Applied to an injury, the animal feeds on damaged tissue and cauterises the wound as it goes, leaving it clean and closed.
It is introduced in the pilot episode Broken Bow, set in 2151. Archer is shot in the leg by the Suliban on Rigel X, and wakes in sickbay to find an eel at work on him. The scene helps to establish Phlox's cheerful faith in treatments that human doctors of the day find alarming.
The eel belongs to the wider menagerie that Phlox maintains in sickbay, alongside creatures such as his Pyrithian bat. His use of animals in medicine reflects the interspecies exchange programme through which he came to be working on Earth.