Jacques "decontaminates" new fish to the tank in the dentist's office. He also controls the "Ring of Fire" on Mount Wannahockaloogie, as seen when Nemo was given a royal welcome by the Tank Gang, who dubbed him "Sharkbait" after he successfully swam through the "Ring of Fire." Later, Jacques activates the "Ring of Fire" again for Gill, who shoots out of the tank and lands on Darla's head (which distracts her while she was shaking the bag that Nemo was in) to save Nemo from becoming Darla's next victim, like her previous fish Chuckles. It is unknown where the dentist got Jacques from.
According to the book Finding Nemo: The Essential Guide, Jacques was one of the pets of the President of France, and given to Dr. Sherman as a gift.