A while ago we acquired a cute microglanis iheringi

At first he(she) was very fat, and we're wondering if we overfed him... (once per day, carnivore pellets, fish, artemia, calf's heart)
Now he's a little skiny... And so we are wondering if he's sick or something else or.. if he's getting old...Because since we've had him, he hasn't grown much...
So my question : what is the lifespan of this fish?