Swollen Gill

Question
I have a 20 gallon tank with several mollies and 3 fancy guppies.  I actually just upgraded from a 10 gallon tank because my mom wanted to get rid of her 20 gallon tank.  Anyway, one of the Mollies my mom gave me with the tank has a swollen gill.  She says that she's had it for a very long time and that it surfaced just before she gave birth to her last batch of fry.  It is only on one side and is a pinkish color underneath.  She seems to be okay, and it's been months, should I be worried?  Is this something that can be healed?  The redness makes me think it's probably tender...

Thanks,
Katie

Answer
Hey Katie,

It's a stress induced infection called gill disease. It's probably not a huge concern, if this fish in particular gets it on a regular basis, I'd just be gentle, soothing, patient, slow, and careful with it. Avoid netting it, chasing it, scaring it, or stressing it with big water changes.

If things dont improve after a few days, consider tetracycline as a treatment. Maracyn-two is another decent treatment for the condition, but maracyn-two is a bit more likely to kill the fry if you add it to their tank.

Hope this helps and best wishes!