Lump on Neon Tetra's stomach?

I have just gotten 6x Neon Tetras less than 24hrs ago. I have been observing them and they seem to be really well, schooling, eating ect. But I have noticed one (male I think) has been chasing the rest, looks like he is nipping. But my concern is his stomach looks mis-shaped compared the rest.

I have tried to take pictures but one side there is a noticeable circular lump. Any ideas?

I have checked the water parameters, no spikes yet, 10 gallons, just 6 neon tetras in the tank. I did quarantine him because I'd rather be safe than sorry

 

Is his stomach like that all the time or just after feeding? I've had a few rummynose that had stomachs that looked like that after feeding. It went away as they grew bigger.

 

This could be one of three things:
1. He ate a little too much.
2. It could be dropsy.
3. He might be a she (pretty unlikely)

 

Is his stomach like that all the time or just after feeding? I've had a few rummynose that had stomachs that looked like that after feeding. It went away as they grew bigger.

Not too sure as I have only just gotten them. I fed them a little last night and this morning (been 4 hours since) I'll keep an eye out to see if it depletes

 

This could be one of three things:
1. He ate a little too much.
2. It could be dropsy.
3. He might be a she (pretty unlikely)

Thank you! Could be a girl. I'm just going off of the straight stripe and it's definitely the smallest, regardless I'll keep an eye out