When fish die for no apparent reason?

[joec]

I've had fish die in the past from disease but I just had a tail spot blenny die all of a sudden for no apparent reason. I quarantine with copper, etc. Established tank is healthy. I've had the TSB for 18 months, he was fat, active and eating yesterday morning. I noticed he was a little lethargic late yesterday and this morning, dead.

? Obviously it could have died of old age, it was almost full grown when I got him.

 

[JSchwarz]

I had a TSB for about a year and a half that just disappeared one day. He was also always very fat and active picking at the rocks and never appeared sick. My other fish have been totally fine for months since. I looked around the tank to see if he jumped even though I have a screen top. I can only assume he died somewhere in the rockwork.

 

[rkpetersen]

Just like people, fish can keel over suddenly without obvious reason.
When I've had fish die like that, on a couple of occasions it's been flukes.
Most of the time, there is no visible explanation, and all the other fish are fine.
Dip the dead fish in freshwater, see if anything floats off.
Another thing you can do is an amateur autopsy. Might be something obvious wrong inside.