Barnaby and his people live in the Great Barrier Reef and were being infected by pollution that caused their fins to rot. Barnaby asked Sabrina and Gwen for help after he discovered that they were witches. In order to protect him, Sabrina cast a spell to give him legs for 48 hours.
Barnaby loved experiencing life as a man, even though he was a bit naive. In the end, Sabrina was able to save Barnaby's family and he was transformed back into a merman.