It could have been Dr. Seuss meets HP Lovecraft:
…I mean, it had the right narrative arc. Naive fool meddles with forces he does not understand, disobeys instructions, gets a horrific result that breaks the very laws of time and space, and disaster is averted at the last second by a mysterious loremaster (who caused the problem in the first place). Potentially good stuff… but there was far too much people getting mad at the kid for having a steadily-growing, monstrous fish; and not nearly enough people going mad at the sight of a steadily growing, monstrous fish.
:pause:
The Sixties were weird, man.
… or something might happen…
… and now you know what. Though the evil that causes it to happen, when your vigilance slips, hides in the darkest corners of your nightmares.