"I could be entirely wrong, but your fish could be suffering from something in the water - either dirty water or something from outside of the tank which is poisoning it. Dirty water/ high nitrogen levels/ a lack of oxygen effect them much the same. Are you doing weekly partial water changes of 25-45% with treated (ideally seasoned) water of the same temperature as that of the tank? Would you do another partial water change?

Is the tank's temperature controlled by a good heater with some water/ air movement to even it out? Is the temperature some where between 76-79 degrees F. Rapid fluctuations in temperature can sometimes stun a fish.

Has your aquarium been set up long? Is the 6-8 week cycling process done? What are your ammonia, nitrite, and nitrate test readings?

So can abrupt changes in water chemistry. Was that female abruptly put in your tan recently? (See Immediate Help and my little ditty on acclimating new fish if this makes little sense to you.)

The symptoms you describe also can apply to a variety of (flukes, first stage parasites of other sorts) which get into the fish's gills and, by sucking blood, deprive them of nourishment and oxygen. You didn't mention here (or in GL, I just looked) the size of your tank. It is kind of a wild gamble, but if you have an antiparasite treatment, you might treat your fish.

The problem with the commercial treatments is that they have antibiotics in them and will trash your nitrogen cycle. If your tank has a glass top, you might be able to treat that female in a gallon bowl. Scale the commercial antiparasite treatment for 1 gallon. If you could put it on the tank so it is heated, cover it with plastic wrap so that she will not jump out and slip an airstone or piece of solid airline tubing in there with a very modest stream of bubbles, you probably could treat her there.

You didn't mention what part of the world you live in. If you were in the Chicago area I'd invite you over to pick up one of two anthelmintics - which can treat fish for parasites and which, unlike antibiotics, will not clobber the beneficial bacteria in an aquarium. Treating for possible parasites, if you can do it, without messing up the filtration system, also has the advantage of also treating the tank mates, who may be infected with the same parasites, if they have any.

(See the discussion on Camallanus and if there is one, on Capillaria, in Immediate Help.)

I wish, off the top of my head, I could be of more help. I agree with you that you female is in big trouble. Try the partial water change. Keep the temperature constant - those two can't hurt. If you have a filter which can take a layer or bag of activated carbon, try that too.

If she is having real difficulty breathing and you think there might be something in her gills, consider the antiparasite treatment. Unfortunately, if you use an antibiotic on your tank, it may kill everything indirectly by destroying the nitrogen cycle."

I promised to try and find more. Today is hectic, appointments are being skipped and I can't do more. However Google for paralyzed fish and see what turns up.

Read myself to sleep last night in a fish health book. They (Burgess, Bailey and Excell) seem to agree that the problem is either poisoning of the water or parasites in the gills.

Once the flurry of activity is down Jman, read the editorial attached to the log submission just before yours - Guppies keep dying. That isn't important now, but would be relevant for new submissions to GL.