Tiger Barb life span

What's the life span for Tiger Barbs?

I was cleaning the tank today and found one dead on the bottom. I think it
must have been dead for at least a couple of days, as it had lost most of
it's colour and most of the head had been pecked away. It was also a little
ripe when I scooped it out. I did a complete water test and everything came
out fine, so he either died of old age or someone did him in. The suspects
include 8 Cardinal Tetras, 5 other Tiger Barbs, 6 Golden Rosy Barbs, 4 SAEs,
3 Yoyo Loaches and an unknown number of Otos.

Should I be concerned about replacing him anytime soon? I know the minimum
number for T' Barbs is about six. But I hate to add new fish, when the tank
has been stable for quite a while. I'm also near the limit for this tank
already, 55 gallons.

TIA.