Mr. Mussels first appeared when the school was doing the school talent show. He scared Albert with his loud voice. When Bea came flying out from the tank, she had a amazing entrance, but Mr. Mussels said she was missing a little special something. The fish flakes can tilted and fell on the stage, making it look like confetti. He gave Bea the part ("Fish Out of Water"). Mr. Mussels got put in a bowl by Milo because he said that his voice scares everybody ("Milo Gets a Ninja").
At Mr. Mussels's drama class, he yelled at his students that everyone has to have a dream, although Milo was the only one in his class who didn't have a dream. When Milo asked Mr. Mussels what happens if you don't have a dream, Mr. Mussels told him that dreams feed the heart and keep you company. He also told him that dreams are so important that if you don't have one, you'll end up cold, hungry, and alone. Later when Milo went to the fridge to get a drink, an imaginary Mr. Mussels appeared, and he led Milo to seeing the bird cage, which made Milo want to free the bird. When Milo failed to, Mr. Mussels, who just awoke from his sleep, found Milo, who was getting dragged back into the tanks by Bea and Oscar. Mr. Mussels questioned Milo if he will sacrifice anything to fly, in which Milo nods. Mr. Mussels told Milo that was a real dream, and that his friends should support him. When Milo found out that the bird could talk, the bird offered Milo, Oscar, Bea and Mr. Mussels a ride on his back so that Milo could fulfill his dreams ("Flying Fish"). Mr. Mussels and Coach Salmons both sang a part of the song Now That I (Don't) Have You ("Two Clams in Love"). When Milo started recycling at Freshwater, he took the toilet papers to recycle them. However, Milo took them while Mr. Mussels was using the bathroom ("Legend of the Earth Troll").
When Oscar was about to take his drivers test, he found out that Mr. Mussels and Coach Salmons were his driving teachers. Oscar didn't really like the fact that two energetic and crazy teachers were his driving teachers, but he got in the car anyways. Mr. Mussels and Coach Salmons told Oscar the rules of driving, and that if he gets 3 "dings", he will fail his driving test. Oscar started driving, and they started out good. But they couldn't figure out how to get back to the DMV. Oscar was about to look at the map how to get out of there, Mr. Mussels snatched the map, saying that he will get one "ding" if he reads while driving, so Mr. Mussels ripped the map, causing the them to be stranded. Mr. Mussels told Oscar that he knew the way out. Coach Salmons suggested that they should ask someone for directions, but Mr. Mussels told him that he knows what he is doing, causing the two to argue for a while. When Oscar drove out of the tanks, Coach Salmons and Mr. Mussels apologized for what they did, and when Oscar asked Mr. Mussels where they are supposed to go, Mr. Mussels said he actually didn't know the way out. So now the three are all lost outside the tanks. Oscar got 2 "dings" when he didn't look at the road, causing Oscar to try to be more careful. After unsuccessfully trying to get directions from Milo, Mr. Mussels and Coach Salmons asked Oscar if they could have a meal at the Burger Bunny restaraunt. When they finished their food, Coach Salmons asked if he can use the bathroom. Oscar turned the car to the side of the hall, but he got 3 "dings" for not using his turn siganl, which means Oscar fails his driving test. Right at that moment, Wilford the cat attacked the car. Oscar drove the car away from the cat, and parallel parked in between two boxes of cat food, which caused the cat to not see them and walk away. They ended up finding the DMV, and Mr. Mussels and Coach Salmons were extremely proud of Oscar for saving them, so they let him pass the driving test. Oscar took a picture with Mr. Mussels and Coach Salmons and received his drivers licence ("Riding in Cars with Fish").
When Oscar did a realistic impression on the Queen of Fish England, he ran into Mr. Mussels, who believed that Oscar really was the queen. So thinking Oscar is the queen, Mr. Mussels took Oscar, Bea, and Milo a ride in his limousine to Fish England. Later when Oscar was about to marry the duke, Mr. Mussels came to the wedding to stop the queen from marrying the duke and marry Mr. Mussels instead. So the wedding officiant told Mr. Mussels and the "duke" (who is Milo in disguise) to compete in a "Slow Jams Rap Battle". Mr. Mussels ended up beating Milo since Milo did his poor impression of Mr. Mussels himself. However, Oscar didn't marry Mr. Mussels after he and Milo went back home with Bea after she interrupted the wedding with a wax sculpture of the queen ("Oscar Makes an Impression"). Mr. Mussels was the one who wrote the "Potatoes for Winter" play. When Bea asked Mr. Mussels if he had anything to say to his students before the play started, he said that he wrote the play with nothing more than words, and that they should all try their best for the play. When Jocktopus was getting stage fright, Mr. Mussels encouraged him a little by saying the true power comes from the heart and not from strength. Later when Bea trapped Jocktopus in the trapdoor, she went to Mr. Mussels and told him that Jocktopus was trying to ruin the stage on purpose. However, Mr. Mussels explained to Bea that one day when Mr. Mussels was typing the script for the play, Jocktopus came to his room and told him how he needed to be a part of the show. So the two secretly practiced and rehearsed for the play, until Jocktopus was truly ready. This caused Bea to go back and fullfill Jocktopus's dream of being part of the show ("Fish School Musical").
Mr. Mussels announced to his students that the school talent show is coming up, and that the winner gets a free coupon book. At the end, Mr. Mussels gave to coupon book to Bea's dance group, who were the winners of the talent show ("Fish Talent Show"). Mr. Mussels auditioned for the Hokey Poke commercial, although he didn't get the part ("Bea's Commercial").