Incidental 41 (named Peterson,Nat,Tucker,Gary Greenfish, and Bastian Roughshark) is a fish who has appeared in various episodes and is one of the most common fish characters in the series. He debuted in "Ripped Pants" and had his first major role in "Plankton's Regular."
Nat is a yellow-tan-colored fish with light lavender lips and a dark lavender dorsal fin.
He has white eyes with black pupils. He has a lavender mouth. He has light green arms and legs and wears faded light blue shorts. His stomach is dark-yellow/green and he is very slender and skinny.
Nat often goes without wearing a shirt or shoes.
Nat works at Snail-Po Headquarters and a variety of other places. He was also a member of the Bikini Bottom Music Lovers Club. His last name is revealed in the episode "Missing Identity" when Norma Rechid addresses him by the surname "Peterson."
In "Plankton's Regular," his most notable appearance, he feigns enjoyment of Plankton's chum in order to fulfill a deal with Karen, Plankton's wife. He is shown to live in a mobile home and apparently possesses great acting skills, as he manages to fend off SpongeBob's persistent attempts to give him a Krabby Patty. However, one can foresee the ending when Nat is forced to taste Mr. Krabs' Krusty Chum and he proclaims that it is the second foulest thing he has ever tasted. The audience can infer that the foulest thing is actually Chum, and Mr. Krabs has thwarted him in that area of food service as well.
At the end of the episode, Nat breaks the news to Plankton and cuts off the deal with Karen, returning the money that she had given him to eat at the Chum Bucket. He is last shown being carted off by medical staff members to have his stomach pumped, which he claims will be the third time he will have visited the doctor on account of Chum.
In the episode "Squid Baby," he yells, My face! My face! Also my leg, but mostly my face!," making a reference to Fred's catchphrase "My leg!"
Nat's name could possibly be based off the word gnat, which is a small, non-biting or biting insect that bears similarities to mosquitoes.
His design is similar to Norton, except his dorsal fin is smoother and his colored differently.
The fourth episode of Bikini Bottom Mysteries uses the name "Nat Peterson" for this fish, as it was the name used by Encyclopedia SpongeBobia at the time.