Gold Gourami Infighting - What to do?

[Kitling]

At my LFS, they had a ~40g tank full of Gold Gourami. I came in to buy one, and ended up walking out with two. An employee told me they were all living peacefully in that tank for a long time and two of them would be a great idea.

Today, it's been about a month since I bought the two gourami, and I'm starting to have some issues.

First of all, I saw them breeding a few days ago, so I think they are different sexes (unless fish perform same-sex breeding behaviors - I don't know). Ever since then it has been going downhill.

Gourami "A" doesn't like gourami "B". When B swims nearby, "A" lashes out and chases B away to the other side of the tank. B never seems to attack the other one. Sometimes, B turns its body in a weird sideways position when it is right next to A. It looks like it's trying to appear submissive? But it doesn't help, as A always attacks.

At night, A likes to rest in a corner of the tank near the surface. B always slowly floats over to where A is and touches with its feelers. Then A notices it and chases B away again. It looks like B is just being curious or friendly, but he is annoying A.

Now, it looks like B has some mild injuries on its face from the attacks. His color is much darker. When the two gourami looked happy, they were a light color that showed off the gold a lot. And now, this one looks darker and is showing off his black stripes.

So, should I get rid of one of them? And importantly, which one?

Note that I have neon tetras, black skirt tetras, and a pleco in the tank, and the gourami ignore ALL of them no matter how close they are. 45g tank.

TL;DR: One gold gourami keeps attacking the other. What to do?

 

[Nightingale]

The dorsal fin of a female gourami tends to be shorter and rounded, while a male gourami's is longer and comes to a point. Females also tend to be slightly larger and have a more rounded belly. However, if these gouramis are not fully mature (which is probably the case, as with a lot of fish we buy from pet stores), then it is more difficult to tell the difference between male and female.

If it turns out that you have two males, male gouramis are territorial and will fight each other, with one possibly killing the other.

Also, making sure there are lots of plants and decorations to break up the line of site within the tank can make the fish less likely to be so aggressive toward each other.