lethargic platies

Question
Hello there,
I'm concerned about the two platies in my otherwise healthy, happy 20 g tank.  These platies were actually born in the tank and have thrived (they are now over a year old), but in the last 2 weeks they have lost weight, become "wiggly", and are prone to rest on the bottom of the tank.  They will move if disturbed by other fish, but otherwise seem to prefer to rest on the gravel. The good thing is that they will eat, though it takes them effort to make it up to the surface for the flakes.  Once they get there, they eat well and then settle back down on the gravel.  The "wigglyness" seems to come and go, but it's almost like they are shivering.  My response so far has to do more frequent water changes and to raise the temp to 80 (it was about 77-78 before).  They seem content, just not their former selves.  What can I do to restore their health?  Any thoughts or advice would be greatly appreciated!  Thank you, A.L.

Answer
Hi A.L,
The behavior you described is often called "Shimmying" and it is a behavior livebearers commonly display when something is not quite right.

You have done good with the temp raise and water changes. The weight loss and listless behavior could be due to old age or internal parasites. (Internal parasites can also be identified by stringy/white poo)

I don't feel confident immediately diagnosing them and recommending a vast treatment regimen. But if these were my fish. I'd keep up the water changes and add some aquarium salt to the tank (pre-dissolve it first) but make sure your other fish can tolerate salt (for example catfish and loaches do not tolerate salt well) do this mild precautionary treatment until you can figure something out about their behavior.

Either way, Shimmying is a stress-symptom that is common with livebearers, who tend to be affected more by certain stressors than most fish.

The best thing to do is keep a close watch on them and try to give them the best care possible.

Best of luck!
Karen~