Dr. Gill Gilliam is a snail disease expert, and snail expert. He only appears in the episode "Once Bitten."
He is an orange fish who wears a white buttoned coat and glasses. He has green lips and (unlike many fish) he has arms and fingers just like SpongeBob.
He appears when everyone panics in the Krusty Krab about having Mad Snail Disease. He then explains to everyone that he is a S.D.E. And S.E. (snail disease expert and snail expert). Then he tells them that there is no such thing as Mad Snail Disease and that it is just a myth. To prove his point, he takes a "small" splinter out of Gary's foot, thereby curing Grouchy Snailitis.