Lumps On Glowlight Tetra

[ballashark bailey]

I have a community tank with lots of varied species. I have about 4 glowlight tetras. Two of them have lumps on there underside. It is just the males that are effected, the females seem fine. The effected fish seem fine otherwise. They are eating well. All other species seem OK. I have recently introduced new black neon tetras and another bala shark. Any help would be much appreciated. thankyou.

 

[WILDER]

How many gallons or litres is the tank.
How many fish and which type,.
Water stats in ammonia, nitrite, nitrate, and ph.
Do you keep any neon tetra.
The lumps on the belly do they look soft like filled with fluid, or hard looking.
Lumps that suddenly appear are usually bacterial.