Dying from old age…

[Pepere]

In truth, nothing dies from old age per se, but from organ systems shutting down…

 

Killifish have fairly short lifespans, and the shoal I have were caught and full sized when I got them. As such I have no idea what their ages are, but I have had them for a year and a half… Some have disappeared, as I used to have 8, and I am down to 4.

It is a densely planted tank, and they love swimming in the dense vegetation.  I can understand one settling to the bottom and being hidden and then the snails cleaning up quickly..

Just this past week I noticed one much less energetic laying on vegetation more…  Then it became more lethargic spending most of its time near the bottom of the tank,,,

 

I transferred it to a quarantine tank and it then progressed to bilateral pop eye, stopped eating and passed.  I had tried Maracyn not expecting much, and I wasnt wrong…. My guess is kidney failure…

no other fish in original tank is showing any signs

Does this sound likely?

 

[Guppysnail]

With nothing being new and nothing changing in the tank I would think along these same lines if it were my tank. 
 

Though I have not kept killi fish I have watched several types of fish age out over the years. What I notice is a myriad of “symptoms” presenting. “Dropsy” bloat being the most common I’ve seen and Popeye / blindness being a close second. 
 

It’s always sad to watch fish age out. I’m sorry you are experiencing this. You provided them wonderful care or they would not have had the quality of life that allowed them to live to age out.