Help! I'm a Fish
The fish potion has no time limit.Or at least it has a longer one than Mac Krill said. How would he know? Has he ever been stuck as a fish forever? (Remember, forever is a long time.) Also, watches rarely run true, especially ones that have been submerged under water for a long time. Chuck's watch was probably behind by a few minutes or seconds, and so their "time" ran out earlier.
Joe and Professor Snape are the same person.They both have the same voice, and they are both obsessed with potions.
Sasha is one of Professor Mac Krill's failed test subjects.Originally, after testing the potion on a person, he found that it was too strong and caused the loss of all human intelligence. Sasha was lost in the same way Stella was; by the time Mac Krill found her, it was too late. She was stuck in that form forever.
The US cover has such god-awful art because the US distributor didn't want it to be a success.Some idiots probably didn't want a non-Disney (or Fox, DreamWorks, WB, whatever) and non-Japanese animated film to have much success in the States. Since CG-animation was popular at the time, they made a CG cover and made it look deliberately terrible to keep people from buying it.
The US cover was a huge Take That toward American animation of the era.This terrible cover was essentially mocking the States' obsession with CG animation over traditional animation. This cover art was also a test to see if Americans wouldn't judge a book by its cover.
This movie was originally going to be part of a six-part anthology corresponding with Merlin's tests in The Sword In The Stone.We know that in The Sword In The Stone, Merlin tests Arthur by transforming him into various animals, the first of which is a fish. This movie revolves around three kids who get turned into fish. This could mean that a series was planned; each title would be Help! I'm a/an [Insert animal name here], and each film would have a different group of kids getting turned into the eponymous animal. It was going to be a combination of tests from the novel version and from the Disney movie. However, this idea never took off, as the movie didn't get a lot of publicity, and the creators feared it would turn into a Franchise Zombie from all the sequels. So, they just abandoned the plans.
They were on drugs the whole time.
The antidote's effect on the fish eventually wore off......resulting in them (slowly?) reverting back to their normal non-speaking states and tying up the last loose end.