Goldfish

[alyss19]

He's in a 2.5 g tank, been alone for about 2 years now, guessing about medium size. He likes to stare out into a corner, the filter used to be there but it got moved...but he still goes to that corner. More often now.
I'm not sure if he's lonely or not, so I put another goldfish in his tank. It's only been about an hour, and he seems to be ignoring the little guy. His name is Bubbles, is he aggressive or lonely?

 

[Lollipops]

Yay! Welcome fellow goldfish mama

They can usually learn to like each other and get along after a time. As long as one''s not chasing the other around, I wouldn't be worried

Are they both the same type, and the same size?

Too much of a size difference and the smaller one might look like a snack for the bigger one!
And if you combine common goldies with fancy ones, they might outswim the fancy ones, who then wont get enough to eat.

Now, I'll beat everyone else to the punch...
How big is your goldfish?

Not matter what, 2.5 gallons is really really really small for a goldfish.
It's a very common, very incorrect misconception that they can live in small spaces... Goldfishes' normal life expectancy is longer than a cat or a dogs, but tends to be cut extremely short, often by small living spaces.

I recently inherited a big ol goldie from a student of mine, in a 10 gallon, and promptly started scouring Craigslist for a cheap used 55 gallon. It's a big tank, but worth it for the sake of the fish... Imagine confining a dog to a walk in closet, instead of letting it roam the house. These fish in particular need space!

I found a 55 gallon for $30 on Craigslist B) Mr. Sunshine is much happier for it!

 

[Delapool]

Plus one on above if 2.5g. Perhaps 25gal?

 

[toolman]

Goldfish need bigger tanks, or a pond!