As a breeder of sterbai cories, sterbai are known to release a toxin from behind their gills when stressed, therefore commiting suicide and taking the rest of the fish in the bag or container to heaven along with them. I had to do a little research on this before I shipped my baby cories. I used a method called "kick the bucket". Before shipping, I'll catch the cories 1st, and kick the bucket every time I pass it. They will release toxins into the water, which you can actually see at the top. It appears as a clear, foamy looking substance at the top. They release most of it into the bucket, so then you change the water, and bag them up. They'll still have some left during shipping, but it is estimated to be less then 20%.
From what I've read, the species that have the most toxins are Sterbai (Sterbai is considered the worst), Arcuatus, Adolfoi, Haroldschwartzi, Burgessi and possibly Robustus. I think if you can ship them while they are still small there is much less chance of the poisoning happening. I shipped many, many small sterbai (approximately 8 weeks old) all across the country without issue. Until I shipped a batch of larger sterbai....which released the toxins and arrived DOA. Shipping fish is stressful enough for me, after this happened I stopped breeding the sterbai. Maybe try the "kick the bucket" method.
Have you found any reference to this happening to black cories from anyone else? I have a group of 10 that I was hoping to breed. I think they are not quite 2 years old. But if they do the same thing for shipping, I'll not be selling any young ones. Redkahuna would be a good one to ask, he has shipped a gazillion cories.
:rofl: 
