The Main Trio
- Voiced by: Chelsea KaneSpecies: Goldfish
The goldfish who lives across the street from Milo and Oscar. She has a strong desire to become an actress superstar, and often plays the lead in her school plays. When she doesn't act as the voice of reason, she can be a control freak.
- Ambiguously Jewish: Her last name, "Goldfishberg", is a pun on the surname "Goldberg", which is a stereotypical Jewish name.
- Birthday Episode: "Bea's Surprise Party".
- Drama Queen: Justified as she's the star pupil of the school's drama department.
- This is also her main flaw, she can get a little to passionate about even the smallest role.
- Determinator: When she sets her mind to something, Bea just won't stop.
- Dude Magnet: In "Doris Flores Gorgeous", she goes on several dates and has gotten the attention of Steve Jackson, the most attractive guy in school. Oscar has also had a huge crush on her for years, along with Randy Pincherson, to her chagrin
- First Girl Wins: She’s been hanging out with Oscar since the start of the show, and they become a couple by series’ end.
- Gamer Chick: She'll occasionally join Oscar and Milo in playing video games.
- Girly Girl with a Tomboy Streak: Despite "Sleepover Party" showcasing her as a stereotypical teenage girl, she still has some masculine interests like football and playing video games with Milo and Oscar.
- Green-Eyed Redhead: She has red hair and, as shown in "Oscar is a Playa", she has green eyes.
- Informed Deformity: She initially thinks her yearbook photo is terrible, citing things like her eyes being too far apart and that she has "fish lips", when in reality her photo looks perfectly fine and is one of the better looking ones out of her class.
- Jerk with a Heart of Gold: Sure, Bea is selfish, desperate to reach her dreams, and suffers from Small Name, Big Ego, but at the end of the day, she actually cares more about her family and friends.
- Large Ham: Justified, since she is an aspiring actress.
- Platonic Life-Partners: With Oscar and Milo until she gets together with the former in the Series Finale.
- Plucky Girl: Bea is cheerful, enthusiastic and rarely gives up when she wants something.
- Pride: She has shown signs of arrogance, such as frequently complimenting herself and thinking that she's too talented to be punched, as "Happy Birthday, Jocktopus" shows.
- Redhead In Green: When she dresses as Oscar in "16 Clamandles".
- Single Girl Seeks Most Popular Guy: The object of her affection in some episodes is the local Pretty Boy heartthrob.
- Single Woman Seeks Good Man: During graduation, she realizes she likes Oscar.
- Small Name, Big Ego: Due to her dreams of becoming famous, she often has a high opinion of herself. Downplayed, considering she can be a good actress and knows she isn't famous now.
- Unwitting Pawn: To Fishington in "Principal Bea".
- Youthful Freckles: Although not that prominent, she has three freckles on each side of her cheeks.
- Voiced by: Kyle MasseySpecies: Siamese fighting fish
A fish who's always looking for some fun. He's usually the class clown, especially in Mr. Baldwin's class. He's always getting his two best friends in many zany adventures, whether they want him to or not.
- Attention Deficit... Ooh, Shiny!: "Fail Fish" implies that he has some sort of attention disability.
- Book Dumb: He is not a good student and he has trouble learning. But one episode showed that he is able to learn new things when he is in danger.
- Blue Is Heroic: He’s light blue with darker blue fins.
- Catchphrase: "Hot dog!"
- Class Clown: In Mr. Baldwin's class.
- Cloudcuckoolander: He's very eccentric and goofy, and is prone to coming up with crazy ideas out of the blue.
- Comedic Underwear Exposure: He is sometimes seen wearing Oscar's underwear for comedic affect.
- The Ditz: He isn't very wise.
- Fat Best Friend: To Oscar and Bea.
- Fat Idiot: A bumbling, obese fish.
- Foil: To Oscar.
- All Work vs. All Play: The All Play to Oscar's All Work. (One of Two)
- Fat and Skinny: The Fat to Oscar's Skinny. Originally it was supposed to be the other way around.
- Red Oni, Blue Oni: The Red to Oscar's Blue.
- Sensitive Guy and Manly Man: The Manly Man to Oscar's Sensitive Guy.
- Fun Personified: Always looking for fun, regardless of the situation.
- Heterosexual Life-Partners: With Oscar, of the brotherly, family variety.
- Ignorant of Their Own Ignorance: He's a stupid goofball and usually the reason for episode conflicts, but actually means well nevertheless.
- Kindhearted Simpleton: His kindness and well-meaning intentions make up for his lack of book smarts.
- Large Ham: He lacks an indoor voice and is prone to overdramatic emphasis.
- Life of the Party: Is usually one to party crazier than anyone else.
- Love Interest: Finberley seems to have a crush on him, seeing as how she once requested to go on a lunch date with him and thinks it's cute when Milo gets all weak.
- Nice Guy: While he isn't very wise, he has a quite friendly and endearing attitude.
- Nice Job Breaking It, Hero: He is usually the cause of conflict.
- No Indoor Voice: Being quiet and him are not on the best of terms.
- Obsessed with Food: He once got hungry in class because Mr. Baldwin's nose apparently looks like a sea cucumber.
- Odd Name Out: Out of the trio, he's the only whose name is not a common one.
- Platonic Life-Partners: With Bea, being one of his best friends.
- Potty Emergency: "Bea Saves a Tree" reveals that he pees in the water rather than the bathroom.
- Trademark Favorite Food: Apples.
- Voiced by: Justin RoilandSpecies: Catfish
A nerdy fish who likes to play video games and roleplay. When Bea isn't the voice of reason, he usually fulfills this role. His brother's antics may make him cranky at times, but he's always got his back. He harbors a secret crush on Bea, but is too shy to admit it.
- All Work vs. All Play: The All Work to Shellsea and Milo's All Play.
- Berserk Button: Just don't let him catch you even touching Bea if you're a jerkass, because he'll be very angry.
- Butt-Monkey: His worries are often a result of his misfortunes.
- Dogged Nice Guy: To Bea.
- Fat and Skinny: The Skinny to Milo's Fat. Originally it was supposed to be the other way around.
- Masculine Girl, Feminine Boy: Feminine Boy to Angela's Masculine Girl
- Meaningful Name: An Oscar is a popular species of aquarium fish.
- Meaningful Rename: When he temporarily joined the goth fish, Oscar changed his name to Bubblethorn.
- Nice Guy: Very nice most of the time.
- Nervous Wreck: And how. He loses his cool over just about everything.
- No Sense of Humor: The "Funny Fish" deals with this.
- Pac Man Fever: His video games usually look very old-fashioned.
- Perky Goth: In the episode where he became one, although he was back to his normal self at the end.
- Pubescent Braces: He wears braces.
- Red Oni, Blue Oni: The Blue to Milo's Red.
- Sensitive Guy and Manly Man: The Sensitive Guy to Milo's Manly Man.
- Stalker with a Crush: To Bea, but he is not as bad as Clamantha.
Other Students
- Voiced by: Kari WahlgrenSpecies: Jewelfish
A jewelfish who's into fashion and being cool. She's Bea's closest friend outside of Milo and Oscar, and is seen occasionally giving advice to her. She loves to gossip and eat.
- All Work vs. All Play: The All Play to Oscar's All Work. (One of Two)
- Beauty Is Bad: She may be attractive, but she's an Alpha Bitch. However it's downplayed in that she's more of a Lovable Alpha Bitch (see below).
- Big Beautiful Woman: As a human in "Pool Party Panic".
- Catchphrase: "Llllllove it!"
- Lovable Alpha Bitch: She is popular and sometimes looks down on Oscar and Milo, but is generally a good friend to Bea.
- Phoneaholic Teenager: She loves chatting on the phone.
- Pink Means Feminine: She’s pink all over.
- Punny Name: Of "Shell" and "Chelsea".
- Valley Girl: She is a stereotypical teenage girl who uses words like "Bae" and "Girl" often.
- Voiced by: Kimberley Mooney
A clumsy fish who can be very emotional and hyperactive at times. She always tries her best to keep a smile on her face.
- Butt-Monkey: She has gotten this status since Season 2.
- Cute Clumsy Girl: She sure is cute, yet clumsy.
- The Cutie: She gets very emotional at times, often leading to cute, Genki Girl momments of Squee.
- Genki Girl: She's one cute and hyperactive fish.
- Girlish Pigtails: Has these.
- Nice Girl: Has a sweet and endearing personality.
- Older Than They Look: She is a teenager but looks like a little girl. Her human counterpart in " Pool Party" further displays this.
- Punny Name: Of "Fin" and "Kimberly".
- Pubescent Braces: She's a teenager and sports braces that, along with her pigtails, make her resemble the "awkward youth" state.
- Running Gag: Getting hurt unintentionally.
- Voiced by: Rachel DratchSpecies: Slug
An awkward slug who's usually the pessimistic one in the group, and Albert Glass' girlfriend.
- Official Couple: With Albert Glass.
- Pink Means Feminine: She wears a pink shirt.
- Punny Name: Of "Escargot" and "Margo".
- Voiced by: Rachel Dratch
A big Koi fish who can only speak in "wuh"s. Compared to her friends, she's surprisingly the most gentle one.
- A Day in the Limelight: "Koi Story".
- Gonk: Her appearance is quite distorted.
- Gonky Femme: She is big and gonky, has a deep voice, and is a Dumb Muscle, but she acts as girly as the rest of her friends.
- Huge Schoolgirl: Serves as the giant one among her little fish classmates.
- Intelligible Unintelligible: Despite having a limited vocabulary, everyone understands what she's saying.
- The Unintelligible: She usually only speaks in limited gibberish.
- Voiced by: Atticus ShafferSpecies: Glass fish
A glass fish who is one of the smartest in his class. He skipped several grades, making him the youngest of his class.
- Butt-Monkey: Jocktopus often bullies him.
- Child Prodigy: Implied. He skipped a few grades and he sounds really young compared to the other students on Freshwater High.
- Grade Skipper: He skipped a few grades, which is why he goes to high school despite being (most likely) a kid.
- Nice Guy: Albert is usually shown to be a pretty friendly guy.
- Vocal Evolution: His voice has gotten deeper near the end of the series due to his voice actor experiencing puberty.
- Voiced by: Steven Christopher ParkerSpecies: Shrimp
A giant shrimp who's a pretty big nerd. He's done many science experiments and is very good at robotics and computers.
- Cloudcuckoolander: Less so than his intelligence would make you think, but he's still an oddball.
- Heterosexual Life-Partners: With Albert Glass.
- Official Couple: With Angela after she breaks up with Oscar.
- The Smart Guy: One of the smartest students in school.
- Voiced by: Alex HirschSpecies: Clam
A kooky clam who serves as captain of the cheerleading team and the editor of the school yearbook. She has the hots for Oscar and isn't afraid to hide it, even when he's taken.
- Ambiguously Human: Compared to the rest of the humans in "Pool Party Panic", her human self looks absurd.
- Clamshells as Mouths: She is depicted speaking by opening her shell.
- Cloudcuckoolander: Being a clam among her mostly-fish students and all, she's very strange...
- Out of Focus: Has far less screentime in the second and third seasons, due to her voice actor going on to create another show.
- Punny Name: Of "Clam" and "Samantha".
- Stalker with a Crush: Towards Oscar.
- Voiced by: Greg CipesSpecies: Red salmon
The most popular boy at Freshwater High School.
- The Ace: He has been shown respect by everyone.
- Big Man on Campus: He is very popular, but mostly comes off as a pretty amiable and easy-going guy.
- Chick Magnet: Many girls, including Bea, find him really attractive.
- Nice Guy: Despite his popularity, Steve is usually friendly to the other students.
- Voiced by: John DiMaggioSpecies: Octopus
An octopus who plays on the school football team. Known to be very aggressive to his fellow classmates and is best friends with Albert Glass. He has a soft side that he rarely shows to anyone.
- Birthday Episode: "Happy Birthfish, Jocktopus".
- The Bully: Of Freshwater High.
- Dumb Jock: He's a complete meathead.
- A Day in the Limelight: "Joctopizza", which has really minimal involvement from the main trio.
- Gonk: He is hands down the ugliest character on the show, and is often regarded as such in-universe.
- Hidden Depths: According to his Fishbook profile, he likes doing chores around the house a bit.
- Hulk Speak: He speaks in this tone of voice.
- Jerkass: Of course, when you're the class bully.
- Jerk Jock: Is very aggressive and disrespectful to his fellow classmates and part of the Freshwater football team.
- Jerk with a Heart of Gold: Sometimes, like in his Odd Friendship with Milo.
- Large Ham: As a result of his aggressiveness and Hulk Speak.
- Non-Standard Character Design: He's obviously taller and bigger than the other fish characters.
- Odd Couple: With Piranhica.
- Official Couple: With Piranhica.
- Punny Name: His name is a play on the words "jock" and "octopus".
- Third-Person Person: He always refers to himself in third person.
- Vitriolic Best Buds: With Albert Glass, as he ruthlessly torments and bullies him.
- With Friends Like These...: He claims to be friends with Albert, yet the latter is frequently on the receiving end of his bullying and torment.
- Would Hit a Girl: He has no qualms about beating up his female schoolmates.
- Voiced by: Laura OrtizSpecies: Piranha
A piranha who is Jocktopus' girlfriend. Her short temper makes her less pleasant than her boyfriend, and that's saying something!
- Cute Little Fang: The cute part is debatable, and they're not really little, but she certainly has fangs.
- Girlish Pigtails: Her usual hairstyle.
- Odd Couple: With Jocktopus.
- Official Couple: With Jocktopus.
- Punny Name: A pun on "Piranha" and "Veronica".
- Puppy-Dog Eyes: Uses this occasionally as a running gag.
- Tiny Tyrannical Girl: Shorter than most of the students, and has an even shorter temper.
- Voiced by: Josh SussmanSpecies: Crab
A narcissistic crab who's extremely wealthy.
- Abhorrent Admirer: Has hit on Bea multiple times and on two occasions forced her to go on a date with him, when she, like most people, cannot stand him.
- Arch-Enemy: To Milo.
- Asshole Victim: He really does deserve all the bad things that happen to him.
- Author Avatar: He strongly resembles his voice actor, Josh Sussman.
- Catchphrase: "I'm Randy Pincherson!"
- He even says it while he's disguised as a Grandma.
- Demoted to Extra: Speaks little in Season 3 and rarely has anything to do in the episodes.
- The Dragon: He'll sometimes assist Jocktopus when it comes to sabotage.
- Expy: Who is a money-obsessed crab that you know from a certain cartoon? Except Randy is worse.
- The Friend Nobody Likes: The student body hates his guts. Not surprising considering his assholic attitude towards them.
- Hate Sink: It's clear he's supposed to be hated for all his slimy actions and mean personality. Piranacha and Jocktopus, despite not being really benevolent, at least have moments of being sympathetic and sometimes hang out with the main group. Randy has next to none of that.
- Jerkass: He's an obnoxious, selfish, Rich Bastard who boasts constantly about his wealth and shows little respect to his fellow classmates.
- Laser-Guided Karma: He'll usually get what's coming to him in most episodes.
- Narcissist: He doesn't care about anyone but himself.
- Penny-Pinching Crab: He is a crab student know chiefly for two things: being very wealthy and being very narcissistic about his wealth. In the episode "Dollars and Fish", he plays the part of the strict, unforgiving loan shark whom Milo gets his money from... and who has no problem pressuring defaulting debtors with his claws.
- Pet the Dog: He's a bastard for sure, but he does help the students on occasion.
- In "Principal Bea," he helps the students take down Nurse Fishington, even though he doubts that the plan would work to Bo Gregory.
- He partakes in helping Coach Salmons feel better about himself when compared to his sister in "Camp Camp" by making the other camp look worse. He also doesn't act like his usual jerkass self at all that episode.
- Rich Bastard: He's very wealthy and acts quite boastful about it.
- Voiced by: Felicia DaySpecies: Angelfish
An angelfish who's the captain of the rivaling Saltwater High Debate Team. She can be introverted at times and is heavy into gaming.
- Accidental Misnaming: When Oscar confronted her at prom over her video game obsession and avoiding him, he accidentally calls her Bea, resulting in them splitting.
- Gamer Chick: She's obsessed with video games.
- Masculine Girl, Feminine Boy: Masculine Girl to Oscar's Feminine Boy.
- Punny Name: Of "Angel" and "Angela", but pronounced "Ayn-gel-a", like an angelfish.
- Second Love: For Oscar in Season 2. They break up in "Fish Prom".
- Voiced by: Lil Twist (Season 3)
A famous pop star with tons of fans. His charming ways bring many fangirls to his side.
- Ascended Extra: Originally started out as just a singer who had no lines outside of singing. He got larger parts as the show went on.
- Expy: He's an in-universe stand-in for Justin Bieber.
Adults
- Voiced by: Dana Snyder
A pregnant seahorse that teaches at Freshwater High. He's had trouble with his social life since 1986, at least until Milo, Oscar, and Bea came along...
- Apathetic Teacher: Due to the idiocy of his students.
- Deadpan Snarker: If his students provoke him with his idiocy, he'll make sarcastic remarks behind their backs.
- Mister Seahorse: He's literally a seahorse and was once pregnant in his life.
- No Name Given: His first name has never been revealed.
- The Slacker: He is sometimes seen sleeping on the job.
- Voiced by: Jennifer Coolidge
A squid who's the school guidance counselor that has some issues of her own. She can be quite absent-minded at times. She has a catfish named Attila that she adores very much.
- Voiced by: Richard SimmonsSpecies: Salmon
The P.E. teacher who encourages having a healthy lifestyle.
- Dark and Troubled Past: It was implied that he's fought in war before, although it was only brought up once.
Miscellaneous
- Voiced by: Vanessa Marshall (Mouse), Kari Wahlgren (Snake)
A pair consisting of a mouse and a snake living together on a terrarium in front of the fish tanks. They usually watch what's happening in them.
- Credits Gag: Their commentary usually serves as one, though sometimes it can be unrelated to the episodes plot, or none at all for a handful of episodes.
- A special one happens at the end of "Pool Party Panic", in which they turn into humans, then pigs and then vegetables before they turn back into their animal selves.
- Odd Friendship: Well, duh. Snakes eat mice.
- Those Two Girls: Always seen together.
- Voiced by: Dana Snyder
The owner of the pet shop the series takes place in. He usually has some antics of his own at the start of the program.
- Non-Standard Character Design: He's photorealistic like the rest of the world, instead of cartoony like the characters.
- Once an Episode: He appears at the beginning of each episode, doing something either related or unrelated to the episode. If he appears anymore afterwards depends.
- Red Baron: He's called "The Big Blue" by Hokey Poke's chief. And seeing what happened between them as shown in "Peopleing", he has a VERY good reason to call him like that.
- The Dreaded: To Chief.