First of all, as I am new here, I wish to say hello to everybody
I have a strange question to ask you: I heard about some corydoras sterbai who could secrete a toxine when they consider they are too many in a tank... I never heard about it before, and I really would like to know if it is possible, or if you do have heard about it yourselves.
I only found this with google research: http://www.drta-archiv.de/Fische/Welse/ ... gift.shtml
But my german is a real pity!
The case I expose here is not mine, but someone who posted in another forum:
He introduced first a 6 corydoras sterbai group in his 300liters tank (with only 2 ancistrus), and everything get well.
About a few weeks later (not immediatly), he reintroduce another juvenil group of 6 (I don't remember the exact number sorry!, but let's say 6 ) and then, after 2 perfect days or something like that, he found one dead cory each day! without external signs of illness or anything... And this during several days till now. The dead corys were always the youngest ones if I remember well.
The parameters were all good, and there wasn't any explaination at first sight.
So, what do you think about the story?
I hope you will help me to understand, because personnaly, I am really in vagueness!
Sorry for my english if it's not too good and thanks for your ideas
The book mentions something about toxins possibly produced when the fish are packed in high densities for transport during export.
It's mostly speculation and hearsay, so I wouldn't go out and buy a book for information like that.
AS a retailer I have come across problems with (particularly) Sterbai packed too heavily in the past.
I believe that many whoesalers used to bag the sterbai for a while then re-bag in fresh water befiore shipping in an attempt to negate this problem
Now that Sterbai are being produced in quantity in Singapore and shipped out weekly there seems to be no problems on arrival to us and we are getting very heavily bagged quantities. Perhaps someone locally might be able to enquire ??
This is deffinately a problem with some species of Corydoras, namely: - C. metae; C.sterbai; and in particular C. trilineatus. As Monty has said it usually occurs when these fish are crouded in a bag. What ever it is they secrete causes foaming on the surface of the water and very quickly the fish show signs of suffering becomming lathargic and breathing heavily.
I usually ask for Corys to be agitated or put in a container before baging and when bagged having them put into new water. This usually cures the problem. I do this as a matter of corse when transporting any Cory.
Thank you for all your answers.
I think the mystery will stuck again! Anyway, if this phenomenon is real, it is quite amazing! I hope we will have a clarification one day, because it is quite fascinating for me to imagine such things possible!
Thank you again for your kindness, and see you soon for some more questions!!!
First of all, as I am new here, I wish to say hello to everybody 
I never heard about it before, and I really would like to know if it is possible, or if you do have heard about it yourselves. 
and thanks for your ideas 
Thank you for all your answers.