Free-Range Children: Never addressed directly, but the guppies walk to school by themselves, with only the Little Fish to watch them. They also tend to go on very improbable field trips for preschoolers, including the planetarium, camping in the woods, and a farm to watch a cow have its baby. Who's signing these permission slips?
Meaningful Name: Molly and Goby are named for small fish similar to guppies, while Gil is named for an imporant part of fish anatomy.
Medium Blending: The characters themselves have CGI bodies and Flash animated facial features. The show also has segments with Flash characters and backdrops.
Mind Screw: The characters are all either mermaids or aquatic life, implying that the series would take place underwater. However, the majority of the settings consist of above-water like aspects such as trees and grass. It could be Justified by the fact that bubbles are often seen rising around them, however in some of the Story sketches the characters are blatantly above water (etc. there is running water in the background, or on the moon) and there are still bubbles rising. Added to this that in the episode "The Moon Rocks!", the spaceship they travel in appears to be rising out of somewhere in Canada.
In the camping episode, they build a bonfire. Underwater.
Pun: The lunch jokes. There's a lot more than that.
Puppy Love: All the characters, notably Molly/Gil, Goby/Deema and Nonny/Oona.
Ruleof Cool: In "Have a Cow!", Goby and Gil are having their carrots stolen by a giant robot rabbit. To get it to leave, they use a giant, rocket, robot carrot. This is lampshaded by Oona; "Makes sense to me!"
Schmuck Bait: Many of the things that happen to Gil are his own fault, and his expression often shows that he knows it.
Sci-Fi Writers Have No Sense of Scale: Averted for a gag, where Gil says that Mecury is the biggest planet, and a small ball, looking like Mercury, bounces past him and Molly. Then he says it's Mars, and a slightly bigger Mars ball bounces by. Next he says Jupiter is the biggest planet... and has to run from a Jupiter boulder.
Tertiary Sexual Characteristics: Averted with the snails, lobsters, crabs, and fish, where there's no physical way to differentiate between the males and females (some females will have hair, however.)
Water Is Air: Hoo boy. There are cars and trucks that make normal engine sounds. There are trees. There are things in the "air" that pretty much stand in for clouds (very non-puffy, but easily mistaken for being clouds that look this way due to the animation style, and if not clouds, what the halibut are they? The background turns colors the sky can be but water should never be. Characters do swim, but mostly hovering over the ground at the exact height they'd be standing if they had legs. It's to the point that when you see someone swim upward or otherwise move as if they are under water, you will say "wait, what?!" Amusingly, though, the Disney Acid Sequencesdo have them more believably underwater.
Your Princess Is in Another Castle: At the end of the movie, Bubble Puppy has been changed back. The end, right? Turns out the witch escaped at the last minute. When Gil and Molly point out that she can't change anyone into frogs, the witch says she still has her original Mean Green Bubble Potion. Cue Oh, Crap from the main cast.