What are your favorite "sleeper" fish?

I'll throw my vote in for bettas, too. My first, Mr. Betta, looked pretty drab in the store when I bought him-- he looked a dull shade of blue all over, and I really only bought him because I felt sorry for him and wanted to give him a proper home I knew he wouldn't have much of a chance of getting elsewhere. Within a week of being in a proper tank, his true colours started to really show. The bland, lifeless blue blossomed into a lovely deep royal blue with a metallic sheen, and he started to grow a wonderful vibrant red on his fins near his body, too. He's a stunning fish now, and he certainly knows it and is very proud of it, haha!
 
another vote for bettas ftw! woot! now i've seen some pretty nice males in petsmart, and i can't even imagine what they'd look like at home! in fact i almost bought one like that today, had to resist though because i didn't have another tank ready for him atm....i'll prob. never see the fellow again but he would be so majestic once properly cared for! he would make some nice offspring, so instead i bought another female. couldn't leave with nothing ;)
 
omg-oodness, i must also say koi. they look absolutely horrible in petsmart. but they soon will develop beautiful, deep colors. or shall i say goldfish in general. i've had dull bronze colored goldies become a majestic flaming-orange color
 
Cherry barbs, mostly because the ones I see sold are young ones.
I remember quite a few years ago looking around the LFS, trying to find some fish I liked. I spotted a tiny little 3 or 4 gallon planted display tank with just one beautiful little red fish in it. I had to ask what it was. Turns out I had walked right past a tank of young cherries without even noticing them. I bought six of them on the spot and they were great little fish. The last of the original 6 died a few months ago, but I have more.
 
Most rainbowfish are sleepers. They are often a dull gray in color at the lfs, but when you take them home with good h2o conditions they become amazing. My experience was with western rainbowfish and the ones from papua new guinea. When I bought them, they were gray with some black stripes but no colors at all. After a day of living in their new tank at home, they showed shades of purple, orange, a bit of green, with the bows from guinea flashing a bright blue every time they get a meal. :p:

As for the anti-sleeper, a red snakehead would get my vote. When they are young, they are mostly orange and yellow color but they lose the colors while they grow. WHen they get larger, they just end up with grey and black. The yellow and the orange completely vanishes. :look:
 
Panchax killies of the genus Aplocheilus . When young they look like dull grey guppies. Wen they get older WOW! Even the females have some nice coloration
 
catfish

I think catfish are a great sleeper fish b/c you have to usually give up watching them w/ the light on. even so they would still have to be a favorite of mine.

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29 gal mixed fw
1 butterfly
1 bichir
1purple spot goby
5 catfish(tsn, indian sun, african silver, syno euruptis, and striped mystus)
 
My favorite are pygmy puffers, least favorite would have to be tetras...tetras are all active in the store in LARGE numbers, but as soon as you bring home your little 6 or 7, they aren't as active...
 
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