Life span of Mollies

Question
How long can I expect Mollies to live?  I have several Mollies of different types.  I purchased them when they were about 6 months old and in good health.  They are now about 3 years old.  One of my Dalmatians died today for no apparent reason.    
It looks healthy, no evidence of injury seemed normal when I fed them last night.  The first thing I did was check water.  No problems.  All of the other fish(approx. 20) are fine.

Answer
Hi Alex,

Three years seems about right, although it depends on whether this molly was a female who gave birth to batches of fry or not. Males of livebearer species in general tend to be more long lived. A heavily bred female will not usually last longer than a couple of years, in my reading and experience.

The key to molly longevity is to keep them in optimum conditions - feed them lots of green foods, keep them in hard and alkaline water, and most (if not all) mollies appreciate a bit of salt added to their water. Anywhere from slightly brackish conditions to seawater are happily accepted by mollies, as long as they are acclimated carefully. As I understand it, the only molly that does equally well in freshwater is the Liberty molly (Poecilia sphenops).

If you haven't seen it yet, have a read of this article:
http://www.wetwebmedia.com/FWSubWebIndex/mollies.htm
It really enlightened me about mollies!

I hope that helps, take care.
Nicole