Unexplained deaths

I have been providing my LFS with larger (sub adult) BN for several years now with no incidents. Yesterday the owner had a question for me which I am at a loss to explain. In a tank which housed my last batch of BN, 3 had recently died for no apparent reason. The owner has 17 tanks at home and is an experienced in fish keeping, far more than I actually, so he would notice anything obvious.

The other inhabitants of the tank are albino cories, mts snails, and some zebra loaches. All seem healthy and there have been no deaths save the 3 BN. The dead BN seemed fine up to their sudden demise. Seemed to be eating well, and the bodies had no discolorations, swellings, obvious parasites, fungus etc. The only change in that tank was the introduction of a couple of other BN from another source. These seem healthy and are still alive.

I have had no issues in any of my tanks, so could this be aggression? I imagine there would have been territorial spats, but enough to cause death? There were evidently no torn fins etc which I would expect in that serious a spat.

At home I feed algae pellets and zucchini/courgette and I'm sure they scrounge some flake that I put in for the mollies. I'm not sure what he feeds, but I know he feeds green beans, and has bog wood in the tanks, and in any case he hasn't had any issues til now.

So, for my own enlightenment, and to keep the LFS happy, does anybody out there have any idea as to what could have happened????

Many thanks!!!!!!!!

shock?

remember shock cant take days to manifest. Check your water parameters and then check his. even the slightest difference can cause a fish to freak out

I would be surprised if it was shock. Those particular BN were there a minimum of 3 weeks and probably longer. I can ask about water parameters, he uses the same hard local water that I do, and it shouldn't be too far off. ( one of the reasons he likes to buy local) Shouldn't of course doesn't mean isn't........ And since it was only fish in that one tank, something may have gone "off". Thanks for the input when you should be enjoying your holiday. Have a good one!

hrmmm, not sure then.

hope you can figure it out. Might be one of those things though