This is a drabble that was requested by Nelja about what happens to the tank fishes after the movie. Takes place after the movie, so logically it has spoilers for the whole movie.
"Nemo, it's time to get up! Hurry, get up or you'll be late!"
"Late? But there isn't any school today, Dad!"
Marlin smiled. "It's not school. We have a very special visitor, and we don't want to keep him waiting!"
"A special visitor? Oh!" Enthusiasm made Nemo wide-awake. He hurriedly got out of bed and rushed around, cleaning himself up in the anemone.
Nemo glanced outside and gasped with joy. "Gill!"
He swam over gleefully to the black, white, and yellow striped fish. Gill seemed reflective and somehow dampened, but seeing Nemo he beamed and seemed to lighten up a bit. "Hey, Sharkbait."
"Gill! Gill! You're here, you're here!" He swam into Gill's fins. "I haven't seen you in so long! You've gotta tell me how you guys got out of the fish tank! How's everyone else? Have they—oh yeah, never mind." Nemo hurriedly kept his mouth shut.
"Hey, it's great to see you again, Sharkbait, but one thing at a time here," Gill chuckled.
A regal blue tang fish swam along from a nearby coral, yawning. " 'Morning, Marlo, how's it going?"
"Dory, Gill's here!"
"Gill's here? Oh, hey, Gill!" Dory waved earnestly, even if she couldn't quite remember if and where she had seen him.
Nemo sighed, and swam over to Dory to give her a few reminders. "Yeah, see? It's Gill…from the fish tank?"
"Oh, a fish tank? Where?" she glanced around.
"No, the one from when you were rescuing me!" he exclaimed. "Sydney, remember?"
"Oh yeah, Sydney!"
"So, we finally get to properly introduce ourselves," Marlin said to Gill. "I've heard a lot about you from Nemo. I can't thank you enough for watching out for him while he was at the dentist's office."
"That kid did most of the lookin' after himself," Gill replied. "All I really did was show him the ropes."
"How did you get out of the tank, anyhow?" Marlin asked. "I heard from Nemo that it was highly advanced technology regulating the tank's environment, so it would've been very hard to get past it."
"Interestingly enough, no. It had some crucial weaknesses that made it malfunction with just a bit of tampering. Goes to show that the most sophisticated isn't necessarily the most foolproof."
"Oh, Dory, Gill's going to tell us the story of how they escaped from the tank!" Nemo swam over to Gill. "C'mon, let's go listen!"
"An escape story? Oooh, I love those!" Dory swam over with Nemo.
With some of his old vigor and craftiness coming back into his expression, he detailed to the fish the account of how they had figured out how to break the supposedly lifetime warranty regulating system, which involved many, many bubbles, much to Bubbles's delight, Peach doing some high wire maneuvers into the corner where the silver box was attached, and some plastic seaweed maneuvering into the thin space between the tank wall and the innards of the AquaScum hub.
"Whoa, that's so, so cool!" Nemo exclaimed. "That would've been so cool to see!"
A trio of juveniles, a butterfly fish, seahorse and pink squid came bobbing along to pick up Nemo for an excursion on their day off.
"Oh, Dad, my friends are here!" Nemo swam over to them.
As Nemo reached them, Sheldon asked him, "Hey, who's that other fish with your dad?"
"He's Gill, one of the fish that helped me escape!" Nemo explained. "I just heard how he escaped from the tank; it was awesome how he and the other tank fish did it!"
"How? What did they do?" Tad asked eagerly.
Nemo waved back to his father and Gill. "I'll be back in a little while! See you later today, Gill!"
Nemo swam on with his friends, retelling in vibrant detail Gill's story.
"He seems to be doing just fine," Gill noted.
"Yeah," Marlin nodded. "He's really turning into a little trooper. He's starting to tell me things I hadn't found out from when I was looking for him!"
He turned to Gill. "So, what have the others been doing since then?"
As he told of what he knew of his tankmates' fates, he was thinking of his own. Since then, after they had gone their own ways, he found himself a bit lost. He had been so bent on getting out of the tank that he really had been at a loss of what he would do once he got out of it. He tried to just go out and swim freely, like he had before had been captured, but somehow it wasn't what he thought it would be, and as he talked, the feeling seemed to deepen.
"…And I think Gurgle's probably still clinging to Jacques out there. I think without him and his cleanly habits Gurgle probably would have opted to go back in the tank," Gill chuckled.
Marlin looked behind him. "It looks like they're all doing fine."
Gill blinked. "What?"
A muffled voice sounded out from behind him.
"Can't hear ya, Peach," Bloat sighed, as Gurgle, Jacques, Bubbles and Deb swam into view.
"Oh, good, we finally caught him," Peach's voice said after a dim 'splootch' as she dislodged her face from Bloat's top. "Honestly, Gill, do you realize how much you've been avoiding us?"
Gill glanced at Marlin. "Wait…did you plan this?"
Marlin shrugged. "It was their idea. They were saying if I or Nemo had told you, you would have left before they could say hi."
"I know you were telling us all about being free to find whatever the ocean has to offer us, but really," Deb shook her head, "it doesn't work if you keep feeling like you're missing a few fish."
"Know what I've found out?" Bubbles proclaimed. "The place to find the most bubbles is wherever you find fish. And the bubbles I like best are when those fish making bubbles are the fish I've found the most bubbles with."
"I shall simply be honest," Jacques said. "I have missed everyone dearly."
"And you know something?" Gurgle asked. "All the other fish out there are absolutely filthy! I'd have to go to the Bahamas to find any fish that even heard of the word 'hygiene'! Compared to them, you and everyone else are immaculate sweeperfish!"
Peach drifted onto a nearby coral and hung from it, right next to him. "And Gill – you've been adrift ever since then. If you really wanted to be off by yourself, you wouldn't be trying so hard."
He looked at all of them. And gradually, the dulled feeling he had faded, replaced with a sense of belonging he had been expecting from the ocean all along.
Being in a box does things to you, he had said back then. He supposed that was still, and always would be, true for all of them.
But for the first time, he realized that it could be a good thing.