Problem with a Molly

Question
Hi Lynda,
I have a 70 litre freshwater tropical tank established for around a year.  The water chemistry seems stable and the latest readings for the parameters I measure were as follows:

Temp:  24C, Ammonia: Zero  Nitrite: Zero  Nitrate: <30ppm ph: 6.9

It is a community tank which includes three mollies. One of these mollies used to be a very dominant active fish which was top of the tank pecking order up until about February time.

At that time she appeared to be getting a clamped down dorsal fin.  I did all the usual water quality checks, added aquarium salt, etc, but no improvement.  Over the last five months her (I think its a she) condition has deteriorated.  She has lost weight and swims in a very strange manner.  Her head is level but her body bends downwards so that her tails is pointing almost vertically down.  She has lost all the finesse in her muscle control and moves by wagging her whole body back and forth.  Her pectoral fins seem unaffected but she seems to have very limited fine movement left in her tail.  She has lost her buoyancy and sinks to the bottom unless swimming hard to raise herself upwards.  She can get to the surface with some effort, but spends most of the time at the bottom dragging her tail around the gravel.  I can hardly recognize her as the fish of 6 months ago!

I am at a complete loss as to what is wrong with her!  My immediate thought was swim bladder disease, but she doesn't seem to match the descriptions of fish with this disease.  I've started to think about more bizarre reasons.  Around February the airpump failed overnight causing an oxygen crash, which sadly killed three of my fish and distressed most of the rest - could she have been brain damaged by this?

I've thought of euthanising her but recently her condition seems to have stabilized. She feeds well, is still very active -  scooting around the bottom of the tank and was one of my original four - I would be very sad to lose her.

Have you ever come across anything like this or have any ideas?  My other two Mollies in this tank seem perfectly healthy and happy.

Thanks for your help,

Mike
(England)

Answer
Hi Mike,
Poor little fish!  I would think it is the lack of oxygen that did this too her.  As long as she is eating, and doesn't seem in any pain, I would let her be, but if you see that she is struggling, and looks sad, then you will have to take her out of her misery.  I know this is the worse thing that can happen to us, as we do get attached, and love our fish.
We lost electricity here a long time ago for 6 days.  We lost it in the middle of the night, and when I woke the next morning, my fish were gasping for air.  I kept throwing buckets of water into the tanks, taking out the water, and pouring it back in...to cut a long story short, I did have a "Jurupari" a earth eating Geophagus, which the lack of oxygen affected.  He never swam the same way, never picked up rocks with his mouth again, but I kept him, and he lived a long happy life.
Keep you little molly, she may have lost some capacity with the lack of oxygen, but if she is eating well, let her live.
Lynda