As A Whole (sans Bubble Puppy and Mr. Grouper)
- Aerith and Bob: All the Guppies except for Molly have rather unusual-sounding names.
- Cheerful Child: Subverted with Nonny, who doesn't smile as much as the others.
- Six Token Band: Molly is Hispanic, Deema is blonde, Oona is Asian, Goby is African-American, Nonny is ginger, Gil is Caucasian, and Zooli is either African or Indian.
- Free-Range Children: Their parents seem to be letting their kids walk to school by themselves (sometimes with a friend) and go on field trips that are sometimes improbable for preschoolers.
- Friend to All Living Things: They can make friends with just about anyone, even a squirrel.
- Gender-Equal Ensemble: 3 boys (Gil, Goby, and Nonny) and 3 girls (Molly, Deema, and Oona). Averted after Zooli joins in Season 5.
- Mr. Imagination: Escpecially during the Story segments at the playground.
- Nice Guy: They're all very friendly and helpful.
- Puppy Love: The most popular are Molly/Gil, Deema/Goby, and Oona/Nonny.
- Six Student Clique
- The Head — Gil
- The Muscle — Goby
- The Quirk — Nonny
- The Pretty One — Oona
- The Smart One — Molly
- The Wild One — Deema
- Token Human: The only merpeople characters in a town full of talking sea creatures.
- Vague Age: Those guppies look like they could be around 5-7.
The host of the show, along with Gil.
- Aerith and Bob
- All-Loving Heroine: She has a lot of friends due to her bubbly personality.
- Ambiguously Brown
- Long Hair Is Feminine
- Meaningful Name: A "molly" is a term used for a member of the fish genus Poecilia, which are closely related to guppies.
- Melismatic Vocals: When she sings.
- Nice Girl: She's friendly with everyone she meets, and likes to think of others first.
- Odd Name Out: The only Bubble Guppy with a common name.
- Red Oni, Blue Oni: She is in between Deema's Red Oni and Oona's Blue Oni.
- She is however the sensitive Blue Oni to Gil's energetic Red Oni.
- True Blue Femininity: Her tail.
- You Gotta Have Blue Hair: Has pale pink hair.
The co-host of the show.
- Cowardly Lion
- Curtains Match the Window: He has blue hair and blue eyes.
- In-Series Nickname: Gilly, used by Molly
- Meaningful Name: What do fish breathe with?
- Odd Name Out: He's the only guppy to have a one syllable name.
- Red Oni, Blue Oni: The energetic Red Oni to Nonny's Blue Oni with Goby in between.
- He is also the Red Oni to Molly's Blue Oni.
- You Gotta Have Blue Hair: Has sapphire blue hair.
The creative guppy boy who loves to tell stories.
- Black Best Friend: To Gil and Nonny.
- Meaningful Name: A goby is a species of small fish, not unlike a guppy.
- Mr. Imagination
- Red Oni, Blue Oni: He is in between Gil's Red Oni and Nonny's Blue Oni.
- He is however the Blue Oni to Deema's Red Oni.
- You Gotta Have Blue Hair: Has indigo hair.
The goofy and dramatic guppy girl whose personality is as big as her hair.
- Catchphrase: "Really?", "Well, you've certainly come to the right place!".
- Cloud Cuckoolander
- Drama Queen
- Fun Personified
- Genki Girl
- Hair of Gold, Heart of Gold
- Improbable Hairstyle: She must use a lot of hair gel.
- Large Ham: She's very hammy.
- Red Oni, Blue Oni: The wild and energetic red oni to Onna's Blue Oni with Molly in between.
- She is also the Red Oni to Goby's Blue Oni.
The sweet-natured guppy girl with a great amount of empathy.
- Cheerful Child
- The Cutie
- Friend to All Living Things
- Girlish Pigtails: Her usual hairstyle.
- Graceful Ladies Like Purple: Purple is her main color.
- Hair Decorations: Her starfish hairclip.
- The Heart
- Nice Girl: Next to Molly, she's probally one of the nicest Guppy in the group, being sweet and gentle.
- Red Oni, Blue Oni: The sensitive Blue Oni to Deema's Red Oni with Molly in between.
- She is,however, the Red Oni to Nonny's Blue Oni.
- You Gotta Have Blue Hair: Has purple hair.
The smart and cautious guppy boy who would rather define the word "basketball" than to play it.
- Ambiguous Disorder
- Blind Without 'Em: Without his scuba mask glasses, he cannot see well.
- Bond One-Liner: Yes, really.Rotten Tomato: (whilst trapped in a ketchup bottle) You got me, but I'll get you next time!
- The Comically Serious: Look at any group shot he's in.
- Dull Surprise: Everything Nonny says is emotionless and flat to go with his persona.
- Fiery Redhead: Inverted.
- In-Series Nickname: Nonners
- Loony Friends Improve Your Personality
- Meganekko: Wears a blue-framed scuba mask which doubles as glasses.
- Non-Action Guy
- Perpetual Frowner: He doesn't smile that much.
- Plot Allergy: He's allergic to dirt. This is, of course, brought up and used in the archaeology episode.
- Red Oni, Blue Oni: The sensitive Blue Oni to Gil's Red Oni with Goby in between.
- He is also the Blue Oni to Oona's Red Oni.
- Redhead In Green
- Sesquipedalian Loquaciousness
- Significant Green-Eyed Redhead
- The Smart Guy
- The Stoic: Only smiles on occasion.
- Stoic Spectacles: Well, goggles, but it's the same idea.
- That Makes Me Feel Angry: "I'm very disappointed."
- When He Smiles: The rare times when he does, it's really cute.
- Wise Beyond His Years
A new member of the guppies, introduced in Season 5.
- Hair Decoration: A blue seashell.
- Prim and Proper Bun: Her usual hairstyle.
- Promotion to Opening Titles: Since Season 5.
- Sixth Ranger: Joins the guppy gang in the fifth season.
- You Gotta Have Blue Hair: Has royal purple hair.
Bubble PuppyThe classroom pet.
- Badass Adorable: Refer to the end of the movie...
- Baleful Polymorph: "In Bubble Puppy's Fin-tastic Fairy Tale Adventure!"
- Precious Puppy
- Team Pet
Mr. GrouperThe best teacher in the world!
- Catchphrase: "Excuse me what time is it?" (a guppy would say "It's time for lunch!"). "Line up, everyone! It's time to go outside!"
- Chameleon Camouflage: He can change his natural orange into a variety of different patterns and colors.
- Cool Teacher
- Mad Libs Catch Phrase: "Let's think about (elements of the episode's topic)."
- Nice Guy: He is a kind and supportive teacher towards his students.
- Palette Swap: Again, he has the ability to change his color on a whim.
- Don't Explain the Joke: Oftentimes after the lunch puns, they'll swim off and proceed to explain exactly why the pun is a pun.
- Greek Chorus: "That's silly!"