I am not familiar with "Sresszyme" but it sounds like another marketing hype
even if it was the piscine equivalent of diazapam or prozac, drugging is no substitute for dealing with the environmental or chemical issues that cause stress.
Fish like humans can vary in their tolerence to stress, how they were captured, and subsequently handled are factors, as well as their treatment once they arrive at the LFS.
Nutition is a big factor in an animals ability to deal with and ward off the effects of stress, then again it might be something as simple as the weak one is naturally introverted and being picked on or getting the least to eat.
While I am by no stretch of the imagination an expert of fish stress and diseases, I really don't think that treating fish with OTC "cure-alls" without knowing what you are dealing with is a good plan. I suspect that in many cases using these products may impart a false sense of well being that is shattered when the animal dies.
Then again sometimes animals die with no apperent cause, it's hard to tell unless you are a qualified ichtyopathologist, and have access to the corpse to perform a necropsy immediatly.
Not much help and not at reassuring I know, and for that iI am sorry. Hopefully someone else has more input, can you post more detailed symptoms. Best of luck with the little guy
