Thanks for your responses Chris.
I guess I'll just keep monitoring the situation.
So far, no change. 3 have it and all the fish seem fine, usual behavior.
water change day tomorrow.
I bought a largish school of black neons a while back ago. I lost some in quarantine that had a dark growth more towards the middle of the body along the stripe. I ended up losing all but three. I rarely lose fish and I couldn't figure out what was on them. Went back to where I bought them and several of the neons had the same condition. Probably will never know what happened.
Well again my lfs came through for me.
When I told him about the black neons he informed me that it is a genetic defect and if I wish I could return them for a refund or exchange but there is nothing to worry about.
Because their upper body is somewhat see through it makes em look like they have a big brain lol.
They are healthy so I am keeping them.
Thanks ChrisK for your replies.
Keep the tank dark for few hours then turn the light on. You may be able to take better pics. Do not spook the fish by accidentally bumping into tank and/or tap on the glass as they may get spooked. I cant see the bump clearly.
Thought an update may be worth while to help others who might face similar issues.
2 of the 3 no longer have the growth on their right side
All are healthy and have prospered in ideal conditions.
I did notice the growth diminish on the 2 that now have no visual signs of the growth.
The last that still has it is one of the largest of the group (of 6) and is very normal in all aspects.
Conclusion is: I waited it out patiently and all are good! It's not always the case and diligence in maintenance and 'fish health care' are of the utmost importance.
Ask questions, don't give up until you understand what is going on in your aqua environment.
The fish, plants, etc. are worth it