A Julii wants to be a top swimmer.

[Chrisk-K]

I bought 7 more julii cories yesterday (they are in a QT). One of them behaves like he's a top swimmer (the guy looks like a male). He occasionally sits at the bottom. Most of time, however, he swims near the top. He even rests at the top of an in-tank UV unit, just 1 inch below the water surface. He doesn't show any signs of a swim bladder problem at all and eats well. Have you seen this kind of cory behavior?

[corlis]

It has been documented that certain internal parasites can affect fish behavior. Some behavioral changes noted were bottom dwelling fish species becoming midwater swimmers. It has been hypothesised that this change in behavior increased the chance of the fish being eaten, by a predator, usually a bird, which allows the parasite to develop its adult stage and thus reproduce. Examples could be Digenetic trematodes (eg liverflukes, though they are not fish parasites)

[briar14]

My 6 Julii Cories maintain rigid bottom dweller habits. Occasionally one will venture to mid tank level and forage the vegetation. Rarely will one quickly dart to the top level of my deep tank. I have a Fancy Guppy that thinks he is a cory and constantly forages the substrate. I have a Neon Tetra that thinks he is a Guppy and hangs out with the other 4 guppies which are constantly foraging at the surface while ignoring the other 6 Neons schooling habits.IMO unusual habits can sometimes develop in a particular fish and do not always signal a illness.You are on top of the situation with the QT

[BambooGoanna]

That's weird. My corys hardly ever leave the bottom. I'd keep a close eye on him.

[abcdefghi]

My peppered corys are regularly off the bottom of the tank, the 2 largest ones typically stay at the bottom, but the 11 smaller ones are regularly off the bottom. Not as near the top as yours, but definitely not strictly bottom level either.

I would say if he is eating and active not to worry all that much.

[rainbowcharmer]

The Juliis in my 75 gal are all over the tank - top to bottom. I have a few that on occasion will school with the tetras - not for long, but they'll meander along with them for a while and then head south to the sand again. I think it's the curiosity in them. :)