Hmmmm.....I'll see if I can dig up any info. I suppose there are alot of variables that come into play here. How old they are when captured, any stresses in the tank like chemistry swings, food source, successful molts, etc.
I have read somewhere (sorry, can't remember where) that the average lifespan of scarlett cleaner shrimp is a little over 3 years. I would guess fire shrimp would be somewhere in that ballpark too...
