Mr. Mussels is a mussel and the drama teacher at Freshwater High. He tries to motivate his students, but yells like a sergeant. He enjoys teaching and singing.
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 an 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' 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 restaurant. 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 signal, 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 license ("Riding in Cars with Fish").
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 did not get the part ("Bea's Commercial").
- He thinks friendship is important.
- He has his own motorcycle, as shown in a short with the Hermit Crab.
- He wants everybody to have a dream ("Flying Fish").
- Mussels cannot be kept as pets.