The cyanide or other toxins issue in fish collection is one of the "dark" areas that we can never know...We are not there to see them collected - nor is the exporter, nor the importer/wholesaler, nor our LFS....so you see my "shadow of doubt" theory about fish - when they die mysteriously.
One thing you can do for new fish - is to feed with Piperazine laced foods for a couple of weeks. This is an excellent wormer, and will help rid the fish of intestinal parasites that can stress the fish, causing it to succumb to illnesses that it may otherwise have been able to shake off. (Tetra makes this as a flake food - you can mix it in with frozen brine to get finicky eaters to try it)
Then, after this round of treatment - you may want to feed a food that includes an anti-biotic, for any secondary infections that can occur because of the parasites.
Hope this helps!
T
One thing you can do for new fish - is to feed with Piperazine laced foods for a couple of weeks. This is an excellent wormer, and will help rid the fish of intestinal parasites that can stress the fish, causing it to succumb to illnesses that it may otherwise have been able to shake off. (Tetra makes this as a flake food - you can mix it in with frozen brine to get finicky eaters to try it)
Then, after this round of treatment - you may want to feed a food that includes an anti-biotic, for any secondary infections that can occur because of the parasites.
Hope this helps!
T